#include <iostream>
#include <fstream>
using namespace std;

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

int n;
int nrz(int n);

int main()
{
    fin >> n;

    int st = 1, dr = 2147483645;

    if(n == 0)
        fout << -1;
            else {
    while(dr - st > 1)
    {
        int mij = (st + dr)/2;

        if(nrz(mij) >= n)
            dr = mij;
            else
                st = mij;
    }
    fout << dr ;}
    return 0;
}
int nrz(int n)
{
    int nr = 0;
    while(n >= 5)
    {
        nr += n / 5;
        n /= 5;
    }
    return nr;
}