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

using namespace std;

int main(){
  int n, count,j;
  int limit;
  vector<int> nl;
  while(cin >> n){
    nl.push_back(n);
  }

  for(int i=0; i<nl.size(); i++){
    n = nl[i];
    int prime[n+1];
    for(j=2; j<=n; j++){
      prime[j] = 1;
    }
    count = 0;
    limit = (int)sqrt(n);
    for(j=2; j<=limit; j++){
      if(prime[j] == 1){
        for(int k=j*2; k<=n; k+=j){
          prime[k] = 0;
        }
      } 
    }

    for(j=2; j<=n; j++){
      if(prime[j]==1){
        count++;
      }
    }
    cout << count << endl;
  }

  return 0;
}