Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextInt() int {
	a, _ := strconv.Atoi(scanner.Text())
	return a
}

func isPrime(n int) bool {
	for i := 2; i*i <= n; i++ {
		if n % i == 0 {
			return false
		}
	}
	return true
}

func main() {
	for scanner.Scan() {
		n := nextInt()
		cnt := 0
		for i := 2; i <= n; i++ {
			if isPrime(i) {
				cnt++
			}
		}
		fmt.Println(cnt)
	}
}

C++: #include <iostream>

using namespace std;

int isprime(int x){
	if(x < 2){
		return false;
	}else if(x==2){
		return true;
	}else{
		for(int i=3;i<x;i=i+2){
			if(x%i==0){
				return false;
			}
		}
		return true;
	}
}
int main(){
	int n;
	while((cin >> n)){
	int a = 0;
	for(int i=2;i<=n;i++){
		if(isprime(i)){
			a++;
		}
	}
	cout << a << endl;
	}
	return 0;
}