#include <iostream>
#include <algorithm>
#include <string>
#include <cctype>
#include <iomanip>
#include <cmath>
using namespace std;
#define MaxN 500000
#define f0(i,n) for(i=0;i<n;i++)
#define f1(i,n) for(i=1;i<n;i++)
char x[MaxN];
int main()
{
    int i=0;
    char c;
    while((c=getchar())!='\n')
    {
        x[i]=c;
        i++;
    }
    long int total=0,t=1;
    int j,k,l,m;
    m=i;
    int count=0;
    int counter;
    f1(i,MaxN)
    {
        if(i<10 && i>=0)t=1;
        if(i<100 && i>=10)t=2;
        if(i<1000 && i>=100)t=3;
        if(i<10000 && i>=1000)t=4;
        if(i<100000 && i>=10000)t=5;
        f0(j,m)
        {
            total=0;
            counter=1;
            for(k=j;k<j+t;k++)
            {
                l=x[k]-48;
                total+=pow(10,t-counter)*l;
                counter++;
            }
            if(total==i)
            {
                count++;
                break;
            }
        }
        if(count==0)
        {
            cout<<i<<endl;
            break;
        }
        count=0;
    }
    return 0;
}
Thanks!!!