#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out")
int nz(int n)
{
    int s=0,p=5;
    while(p<=n)
    {
        s=s+n/p;
        p=p*5;
    }

    return s;
}
int main()
{
    int c=1,p;
    fin>>p;
    while(nz(5*c)<=p)
    {
        c++;
    }
    if(nz(5*(c-1))==p)
    {
        fout<<5*(c-1);
    }
    else
        fout<<-1;

    return 0;
}