#include <bits/stdc++.h>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");

int p=0,s=1;

int main()
{
    in >> p;
    if(p==0) out << 1;
    else{
        int n = 3;
        while(p){
            s*=n;
            while(s%10==0) s/=10,p--;
            s%=10;
            n++;
        }
        out << n-1;
    }
    return 0;
}