#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    long long n,i=0;
    int cnt=0,aux,knt=0;
    in >>n;
        if (n<0)
        {
            out <<-1;
            return 0;
        }
        if (n==0)
        {
            out <<1;
            return 0;
        }
        while (cnt<n)
        {
            i++;
            aux=i;
            while (aux%5==0)
            {
                cnt++;
                aux=aux/5;
            }
        }
    out <<i;
    return 0;
}