#include <iostream>
#include <fstream>
#include <cstdio>
#include <cassert>
#include <complex>
#include <cmath>
#include <algorithm>
#include <vector>
#include <string>
#include <cstdlib>
#include <cstring>
#include <iomanip>
#include <numeric>
#include <sstream>
#include <ctime>
#include <cctype>
#include <set>
#include <map>
#include <queue>
#include <bitset>
#include <deque>
#include <stack>
#include <memory.h>
using namespace std;
typedef long long ll;
#define mp make_pair
const int MAXN =1500;

struct bign
{
    int len, s[MAXN];
    bign ()
    {
        memset(s, 0, sizeof(s));
        len = 1;
    }
    bign (int num) { *this = num; }
    bign (const char *num) { *this = num; }
    bign operator = (const int num)
    {
        char s[MAXN];
        sprintf(s, "%d", num);
        *this = s;
        return *this;
    }
    bign operator = (const char *num)
    {
        for(int i = 0; num[i] == '0'; num++) ;  //ȥǰµ¼0
        len = strlen(num);
        for(int i = 0; i < len; i++) s[i] = num[len-i-1] - '0';
        return *this;
    }
    bign operator + (const bign &b) const //+
    {
        bign c;
        c.len = 0;
        for(int i = 0, g = 0; g || i < max(len, b.len); i++)
        {
            int x = g;
            if(i < len) x += s[i];
            if(i < b.len) x += b.s[i];
            c.s[c.len++] = x % 10;
            g = x / 10;
        }
        return c;
    }
    bign operator += (const bign &b)
    {
        *this = *this + b;
        return *this;
    }
    void clean()
    {
        while(len > 1 && !s[len-1]) len--;
    }
    bign operator * (const bign &b) //*
    {
        bign c;
        c.len = len + b.len;
        for(int i = 0; i < len; i++)
        {
            for(int j = 0; j < b.len; j++)
            {
                c.s[i+j] += s[i] * b.s[j];
            }
        }
        for(int i = 0; i < c.len; i++)
        {
            c.s[i+1] += c.s[i]/10;
            c.s[i] %= 10;
        }
        c.clean();
        return c;
    }
    bign operator *= (const bign &b)
    {
        *this = *this * b;
        return *this;
    }
    bign operator - (const bign &b)
    {
        bign c;
        c.len = 0;
        for(int i = 0, g = 0; i < len; i++)
        {
            int x = s[i] - g;
            if(i < b.len) x -= b.s[i];
            if(x >= 0) g = 0;
            else
            {
                g = 1;
                x += 10;
            }
            c.s[c.len++] = x;
        }
        c.clean();
        return c;
    }
    bign operator -= (const bign &b)
    {
        *this = *this - b;
        return *this;
    }
    bign operator / (const bign &b)
    {
        bign c, f = 0;
        for(int i = len-1; i >= 0; i--)
        {
            f = f*10;
            f.s[0] = s[i];
            while(f >= b)
            {
                f -= b;
                c.s[i]++;
            }
        }
        c.len = len;
        c.clean();
        return c;
    }
    bign operator /= (const bign &b)
    {
        *this  = *this / b;
        return *this;
    }
    bign operator % (const bign &b)
    {
        bign r = *this / b;
        r = *this - r*b;
        return r;
    }
    bign operator %= (const bign &b)
    {
        *this = *this % b;
        return *this;
    }
    bool operator < (const bign &b)
    {
        if(len != b.len) return len < b.len;
        for(int i = len-1; i >= 0; i--)
        {
            if(s[i] != b.s[i]) return s[i] < b.s[i];
        }
        return false;
    }
    bool operator > (const bign &b)
    {
        if(len != b.len) return len > b.len;
        for(int i = len-1; i >= 0; i--)
        {
            if(s[i] != b.s[i]) return s[i] > b.s[i];
        }
        return false;
    }
    bool operator == (const bign &b)
    {
        return !(*this > b) && !(*this < b);
    }
    bool operator != (const bign &b)
    {
        return !(*this == b);
    }
    bool operator <= (const bign &b)
    {
        return *this < b || *this == b;
    }
    bool operator >= (const bign &b)
    {
        return *this > b || *this == b;
    }
    string str() const
    {
        string res = "";
        for(int i = 0; i < len; i++) res = char(s[i]+'0') + res;
        return res;
    }
};

istream& operator >> (istream &in, bign &x)
{
    string s;
    in >> s;
    x = s.c_str();
    return in;
}

ostream& operator << (ostream &out, const bign &x)
{
    out << x.str();
    return out;
}
bign dp[1800][2];
bign k;
int n;
int main()
{
    cin>>n>>k;
    dp[0][0]=k-1;
    dp[0][1]=0;
    for(int i=1;i<n;i++){
        dp[i][0]=(k-1)*(dp[i-1][0]+dp[i-1][1]);
        dp[i][1]=dp[i-1][0];
    }
    cout<<dp[n-1][0]+dp[n-1][1];
    return 0;
}

my bigint struct
hope will help
const int T=400, MOD=10000000;
struct bigInt
{
    int a[T], n;
    bigInt(){};
    bigInt(int x)
    {
        memset(a, 0, sizeof a);
        n = 1, a[0] = x;
    }
    void init(int x)
    {
        n = 1;
        a[0] = x;
    }
    bool operator < (const bigInt &x)
    {
        if (n < x.n) return 1;
        else if (n > x.n) return 0;
        for (int i=n-1; i>=0; i--)
            if (a[i] < x.a[i]) return 1;
            else if (a[i] > x.a[i]) return 0;
        return 0;
    }
    bigInt operator * (const bigInt &x)
    {
        bigInt t(0); t.n = x.n + n - 1;
        for (int i=0; i<n; i++)
            for (int j=0; j<x.n; j++)
                t.a[i+j]+=a[i]*x.a[j];
        for (int i=0; i<t.n; i++)
        {
            t.a[i+1]+=t.a[i]/MOD;
            t.a[i]%=MOD;
        }
        if (t.a[t.n]) t.n++;
        return t;
    }
    bigInt operator + (const bigInt &x)
    {
        bigInt t(0); t.n = max(x.n, n);
        for (int i=0; i<t.n; i++)
        {
            t.a[i] = t.a[i] + x.a[i] + a[i];
            t.a[i+1]+=t.a[i]/MOD;
            t.a[i]%=MOD;
        }
        if (t.a[t.n]) t.n++;
        return t;
    }
    void print()
    {
        printf("%d",a[n-1]);
        for (int i=n-2; i>=0; i--) printf("%07d",a[i]);
        puts("");
    }
};
Ps:this will only work with the + operator. To get AC, I changed the base from 10000 to 10000000, so the * operator won't work.