#include <iostream>
#include <fstream>

using namespace std;

int main () {

	int N, nr = 0;

	ofstream outFile ("ciur.out");
  ifstream inFile ("ciur.in");

  inFile >> N;
  int A[N];

  for(int i = 2; i <= N; i++){
    A[i] = 1;  // Initialy all set to true. 
  }

  for(int i = 2; i <= N; i++){
    if(A[i] == 1){
      nr++;
      for(int j = i * i; j <= N; j += i){
        A[j] = 0;  
      }
    }
  }


  outFile << nr;
	return 0;

}