#include <iostream>
#include <fstream>
using namespace std;

int desc5(int i)
{
    int n=0;
    while(i%5==0)
    {
        n++;
        i/=5;
    }
    return n;
}

int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    int p,n=1,z=0;
    in>>p;
    while(z<p)
    {
        z+=desc5(n);
        n++;
    }
    if(z==p)out<<n;
    else out<<"-1";
}