#include <iostream>
#include <stdio.h>

using namespace std;

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

int cautbin(int p) {
  int st, dr, z, sol, mij;
  st = 1;
  dr = p * 5;
  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() {
  FILE *fin, *fout;
  int p;

  fin = fopen("fact.in", "r");
  fscanf(fin, "%d", &p);
  fclose( fin );

  fout = fopen("fact.out", "w");
  fprintf(fout, "%d", cautbin(p));
  fclose( fout );
  return 0;
}