#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;

int countPrime(int n) {
  int count = 0;
  if(n == 1) {
    return 0;
  }
  bitset<n+1> v;
  for (int i = 2; i <= n; i++) {
    if(!v[i]) {
      count++;
      for (int mult = 2; mult * i <= n; mult++) {
        v[mult*i] = 1;
      }
    }
  }
  return count;
}

int main() {
  ifstream in("ciur.in");
  ofstream out("ciur.out");
  int N;
  in >> N;
  out << countPrime(N);
  return 0;
}