#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");

int n = 1,p1,p;
int main()
{
    f>>p1;

    while(p < p1)
    {

        int nr5 = 0 ,copien = n;
        while(copien%5 == 0)
        {
            copien/=5;
            nr5++;
        }
        p += nr5;
        if(p1 != p)
            n++;
    }

    if(p == p1)
        g<<n;
    else
        g<<-1;

    return 0;
}