#include <iostream>
#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{
    int p,n=1,c5=0;
    f>>p;
    if (p<0) g<<-1;
    else {
        while (c5<p) {
            int n1=n;
            while (n1%5==0) {
                c5++;
                n1/=5;
            }
            n++;
        }
        g<<n-1;
    }
}