#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int n, p, st, dr, m;

int zero(int x)
{
    int nr=0;
    int p=5;
    while(x/p>0)
    {
        nr=nr+x/p;
        p=p*5;
    }
    return nr;
}

int main()
{
    fin>>p;
    st=1; dr=p*5;
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(zero(m)>=p) dr=m-1;
        else st=m+1;
    }
    if(zero(m)==p) fout<<m<<"\n";
    else fout<<"-1"<<"\n";
    return 0;
}