#include <iostream>
#include <fstream>
using namespace std;
ifstream f ("fact.in");
ofstream g ("fact.out");
int main()
{
    int n,i,c,cop;
    f>>n;
    if(n==0)
        g<<0;
    else
    if(n==5)
        g<<-1;
    else
    {
        c=n*5;
        if(n>4)
        {


        n=n-n%5;
        while(n%5==0)
        {
            n=n/5;
            c-=5;
        }
        }
        g<<c;
    }
    return 0;
}