kfact

#include <fstream>
using namespace std;
/// 25 -> 15511210043330985984000000

int nrcifre(int n)
{
    int nr=0;
    while(n)
        ++nr,n/=10;
    return nr;
}

int main()
{
    int n,k;
    ifstream f("kfact.in");
    f>>n>>k;
    f.close();
    ofstream g("kfact.out");
    if(n==0)
    {
        g<<-1;
        return 0;
    }
    unsigned long long int MOD=10000000000,fact=1;
    for(int i=1;i<=n;++i)
    {
        /// g<<fact<<'*'<<i<<" = ";
        fact=fact*i;
        /// g<<fact<<endl;
        while(fact%10==0) /// Renunt la zerouri
            fact/=10;
        fact%=MOD;
    }
    int nrcif=nrcifre(fact);
    if(nrcif<k)
    {
        g<<-1;
        return 0;
    }
    for(int i=1;i<k;++i)
        fact/=10;
    g<<fact%10;
    return 0;
}