#include<iostream>

using namespace std;

int main(){

int data[1000000];


 for(int i = 0; i < 1000000; i++) data[i] = 1;

 for(int i = 2; i*i < 1000000; i++){
   if(data[i] == 1){
     for(int j = i*2; j < 1000000; j+=i) data[j] = 0;
   }
 }
 int in;
 
 while(cin >> in){
   
   int sum = 0;
   for(int i = 2; i <= in; i++){
     if(data[i] == 1) sum++;
   }
   
   cout << sum <<endl;
 }
 return 0;
}