#include <iostream>
#include <fstream>
using namespace std;
const int MAXN = 5e8;
ifstream fin ("fact.in");
ofstream fout ("fact.out");
int nr_zero(int n){
  int s = 0, p = 5;
  while(p <= n){
    s = s + n / p;
    p *= 5;
  }
  return s;
}
int bs(int n){
  int st = 1, dr = MAXN, m, nrz, nr;
  while(st <= dr){
  int m = ( st + dr ) / 2;
  nrz = nr_zero( m );
  if( n <= nrz ){
    dr = m - 1;
    nr = m;
  }
  else
    st = m + 1;
  }
  return nr;
}
int main()
{
    int n;
    fin >> n;
    fout <<  bs(n);
    return 0;
}