#include <bits/stdc++.h>

using namespace std;

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    int p,k=0;
    f>>p;
    if (p==0) {g<<1;return 0;}
    while (p>0)
    {
        k+=5;
        int s=0;
        int inloc=k;
        while (inloc%5==0&&inloc>0)
        {
            s++;
            inloc/=5;
        }
        p-=s;
    }
    if (p<0) g<<-1;
    else g<<k;
    return 0;
}