#include <fstream>
#include <vector>

using namespace std;

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

int primes(int n){
  int count = 0;
  vector<int> v(n + 1, 1);
  for(int i = 2; i <= n; i++){
    if(v[i] == true){
      count ++;
      for(int j = i; j <= n; j += i)
        v[j] = false;
    }
  }
  return count;
}

int main(){
  int n;
  cin >> n;
  cout << primes(n) << '\n';
}