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