#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;

int main(void){
  int n;
  while(cin >> n){
    if(n < 3){
      if(n < 2){
	cout << 0 << endl;
      }else{
	cout << 1 << endl;
      }
    }
    for(int i = 3; i <= n; i += 2){
      bool flag = true;
      for(int j = 3; j <= sqrt(i); j += 2){
	if(i % j == 0){
	  flag = false;
	}
      }
      if(flag)
	ans++;
    }
    cout << ans << endl;
  }
  return 0;
}