#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;

#define NMAX 2000005
char A[NMAX];

int main () {

	int N, nr = 0;

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

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

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

  for(long i = 2; i <= N; i++){
    if(A[i] == 0){
      nr++;
    }
  }

  outFile << nr;
	return 0;

}