#include <fstream>

using namespace std;

const int VMIN = 1;
const int VMAX = 5e8;

int nr_zero(int n)
{
    int nr = 0;
    while (n >= 5)
    {
        nr += n / 5;
        n /= 5;
    }
    return nr;
}

int caut_bin(int p)
{
    ///cautam binar cel mai mic numar alcarui factorial are cel putin p zerouri la final
    int st = VMIN, dr = VMAX, rez = VMAX + 1;
    while (st <= dr)
    {
        int m = (st + dr) / 2;
        if (nr_zero(m) >= p)
        {
            rez = m;
            dr = m - 1;
        }
        else
        {
            st = m + 1;
        }
    }
    return rez;
}

int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    int p;
    in >> p;
    int n_0 = caut_bin(p);
    if (nr_zero(n_0) > p)
    {
        n_0 = -1;
    }
    out << n_0 << "\n";
    in.close();
    out.close();
    return 0;
}