#include <fstream>
#include<iostream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long p,nr;
int n;
int exp(int n)
{
    long long ok=0;
    while(n%5==0){ok++;n=n/5;}
    return ok;
}
int main()
{
    fin>>p;
    n=1;
    nr=0;
    if(nr==p)fout<<n;
    else{n=0;
    while(nr<p)
    {
        n+=5;
        nr=nr+exp(n);
    }
    if(nr>p)fout<<-1;
    else fout<<n;
    }
    return 0;
}