#include <iostream>
#include <vector>

using namespace std;

class Prime {
// n以下の素数を列挙する
public:
  const int n;
  vector<bool> is_prime;
  vector<int> primes;
  Prime(int size) : n(size), is_prime(n+1, true) {
    is_prime[0] = false;
    is_prime[1] = false;
    for (int i = 2; i <= n; ++i) {
      if (!is_prime[i]) continue;
      primes.push_back(i);
      int tmp = 2*i;
      while (tmp <= n) {
        is_prime[tmp] = false;
        tmp += i;
      }
    }
  }

  bool check(int x) { return is_prime[x]; }
};

int main() {
  Prime prime(1000001);
  int n;
  while (cin >> n) {
      int ans = 0;
      for (int p : prime.primes) {
          if (p > n) break;
          ++ans;
      }
      cout << ans << endl;
  }
}

