#include<iostream>
using namespace std;

int main(){
  bool p[1000000];
  int num[1000000];
  int c,n;

  for(int i=0;i<1000000;i+=2)p[i] = false;
  for(int i=1;i<1000000;i+=2)p[i] = true;
  p[1] = false;
  p[2] = true;

  c = 3;
  while(c < 1000){
    for(int i=3*c;i<1000000;i+=2*c)p[i] = false;
    do{c+=2;}while(!p[c]);
  }

  c = 0;
  for(int i=0;i<1000000;i++){
    if(p[i])c++;
    num[i] = c;
  }

  while(cin >> n)cout << num[n] << endl;
}