#include <iostream>
#include <vector>
#include <fstream>
#include <string.h>

using namespace std;
const int Nmax = 2000666;

char isprime[Nmax];

int main() {
  ifstream fin ("ciur.in");
  ofstream fout ("ciur.out");

  int N, ans = 0;
  fin >> N;
  memset(isprime, 1, N+1);
  for (int i = 2; i*i <= N; ++i) {
    if (isprime[i]) {
      for (int j = i*i; j <= N; j += i)
        isprime[j] = 0;
    }
  }

  for(int i = 2; i <= N; ++i)
    ans += isprime[i];

  fout << ans << endl;

  return 0;
}