#include <iostream>
#include <fstream>

using namespace std;

int main () {

     int p, n = 1, f = 1;

     ifstream in ("fact.in");
     in >> p;
     in.close();

     for (int i = 1; i <= p; i++) {
          n *= 10;          
     }

     for (int i = 1; i <= p; i++) {
          f *= i;

          if (f % n == 0) {
               ofstream out ("fact.out");
               out << i;
               out.close();
          }
     }

     return 0;
}