#include <iostream>
#include <fstream>
using namespace std;
ifstream f ("fact.in");
ofstream g ("fact.out");
int putere (long long n)
{
    int co=0;
    while (n%5==0)
    {
        n=n/5;
        co++;
    }return co;
}
int main()
{int i=5,n=5,p,contor=0,ci;
f >>p;
while (contor <p)
{
    contor=contor+putere(i);
    i+=5;
    n++;
}if (contor==p)
    g <<i-5;
else
g<<"-1";
    return 0;
}