#include <bits/stdc++.h>

using namespace std;

#define debug(x) cerr << #x << " = " << x << "\n";

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

const int max_n = (int)2e6 + 5;

int n;

bitset<max_n> prime;

int main() {
  in >> n;
  for (int i = 2; i * i <= n; i++) {
    if (prime[i] == 0) {
      for (int j = i * i; j <= n; j += i) {
        prime[j] = 1;
      }
    }
  }
  int cnt = 0;
  for (int i = 2; i <= n; i++) {
    cnt += !prime[i];
  }
  out << cnt << "\n";
  return 0;
}