#include<iostream>
#include<string>
#include<algorithm>
using namespace std;

int main(){
  bool prime[1000000] = {};
  int sum[1000000]; sum[0] = sum[1] = 0; sum[2] = 1;
  for(int i = 3 ; i < 1000000 ; i += 2 ){
    sum[i] = sum[i + 1] = sum[i - 1];
    if(!prime[i]){
      for(int j = i + i + i ; j < 1000000 ; j += i + i ){
        prime[j] = true;
      }
      sum[i]++;
      sum[i+1]++;
    }
  }

  int n;
  while(cin >> n){
    cout << sum[n] << endl;
  }
}

