#include <fstream>

using namespace std;

int nrz(int x) {
  int put5 = 5, sol = 0;
  while (put5 <= x) {
    sol += x / put5;
    put5 *= 5;
  }
  return sol;
}

int cautbin(int p) {
  int st, dr, z, sol, mij;
  st = 1;
  dr = 2000000000;
  while (st <= dr) {
    mij = (st + dr) / 2;
    z = nrz(mij);
    if (z >= p) {
      sol = mij;
      dr = mij - 1;
    }
    else
      st = mij + 1;
  }
  return sol;
}

int main() {
  ifstream cin ("fact.in");
  ofstream cout ("fact.out");
  int p;
  cin >> p;
  cout << cautbin(p);
  return 0;
}