#include <fstream>
#include <iostream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long factorial(int n)
{long long p=1;
for(int i=2;i<=n;i++)p*=i;
return p;
}
int nrcifre(long long n)
{int k=0;
while(n){if(n%10==0)k++;else break;n/=10;}
return k;
}
int main()
{
    int P;
    f>>P;
    for(int i=1;;i++)if(nrcifre(factorial(i))==P){g<<i;break;}

    return 0;
}