#include <iostream>
#include <cmath>

typedef long long LL;
using namespace std;

const int X = 1000001;
bool Find[X];

void init(){
  for(int i=0;i<X;i++){
    Find[i] = false;
  }
  for(int i=2;i<=sqrt(X);i++){
    if(Find[i])continue;
    for(int j=i+1;j<X;j++){
      if(Find[j])continue;
      if(j%i==0)Find[j]=true;
    }
  }
}

int main(){
  init();
  int n;
  while(cin >> n){
    int answer = 0;
    for(int i=2;i<n+1;i++){
      if(!Find[i])answer++;
    }
    cout << answer << endl;
  }
  return 0;
}