#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    int n, p, ok, i, fact, c, nr, cfact;
    ifstream f("fact.in");
    ofstream g("fact.out");
    f >> p;
    n = 1;
    ok = 1;
    fact = 1;
    while (ok = 1){
        for (i=1;i<=n;i++){
             fact = fact * i;
        }
        cfact = fact;
        while(cfact % 10 == 0){
        nr = nr + 1;
        cfact = cfact / 10;
        }


      if (nr == p){
        ok = 0;
        g << n << "\n";
      }
      n = n+1;
    }
    f.close();
    g.close();
    return 0;
}