#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

int nr0(int n)
{
    int nr = 0;
    while (n >= 5)
    {
        nr += n/5;
        n /= 5;
    }
    return nr;
}

int main()
{
    int pas = 1<<28, p, r = 0;
    f >> p;
    while (pas != 0)
    {
        if (nr0(r + pas) < p)
            r += pas;
        pas /= 2;
    }
    r++;
    if (nr0(r) != p)
        r = -1;
    g << r;
    return 0;
}