#include <bits/stdc++.h>
using namespace std ;

#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
#define mem(x,val) memset((x),(val),sizeof(x))
#define all(x) x.begin(),x.end()
#define pb push_back
#define mp make_pair
#define PI acos(-1.0)

const int INF = 1 << 29 ;
typedef long long ll ;

int N(int n  , int k ) {
    if(n == 1) return k<10?1:0 ;

    int sum = 0 ;
    for(int i = 0 ;i<= 9 && i<=k ; i++){
        sum+=N(n-1 , k-i) ;
    }
    return sum  ;
}

int main() {
    int n ,sum = 0 , temp  ;

    scanf("%d" ,&n) ;
    n/= 2 ;

    for(int i = 0 ; i<=n*9 ;i++){
        temp = N(n,i) ;
        sum+=(temp*temp) ;
    }

    printf("%d\n" , sum) ;

    return 0 ;
}

Thx a lot!
I see it the same method as in http://ega-math.narod.ru/Quant/Tickets.htm
its a pity, but i dont understand it(