#include <fstream>

using namespace std;

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

 int check (long long  n) {
  int p = 5,rez=0;
  while( n >= p) {
	rez += n/p;
	p *= 5;
  }
  return rez;
 }
int main()
{

  long long st = 0, dr = 100000000,sol,put;
  in>>put;
  while(st <= dr) {
	 int mij = (st + dr) >> 1;
	 if(check(mij) < put) {
		 st = mij+1;
      }
     else
	    if(check(mij) > put) {
		   dr = mij-1;
        }
        else {
	         sol = mij;
	         dr = mij-1;
          }
    }
    out<<sol;
    return 0;
}