#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
int main()
{
  int p, n, b;
  ifstream f("fact.in");
  ofstream g("fact.out");
  f >> p;
  n = 5 * p;
  b = 1;
  while (n > 25 * b) {
    n -= 5 * (int)(log (b) / log (5));
    b++;
  }
  if (n % 5 == 0) g << -1;
  else g << n;
  f.close ();
  g.close ();
  return 0;
}