Go: package main

import "fmt"

func main() {
	const MAX = 1000000
	prime := make([]int, MAX, MAX)
	check := make([]int, MAX, MAX)
	count := make([]int, MAX, MAX)

	prime[0] = 1
	prime[1] = 1

	// prime init
	for i := 2; i < MAX; i++ {
		if check[i] == 1 {
			continue
		}

		if prime[i] == 0 {
			for j := i * 2; j < MAX; j += i {
				check[j] = 1
				prime[j] = 1
			}
		}
	}

	for i := 2; i < MAX; i++ {
		cnt := 0

		if prime[i] == 0 {
			cnt = 1
		}

		count[i] = count[i-1] + cnt
	}

	for {
		var input int
		inputCount, _ := fmt.Scanf("%d", &input)
		if inputCount != 1 {
			break
		}

		fmt.Println(count[input])
	}
}

C++: #include <iostream>
#include <cstring>
using namespace std;
const int maxn=1000010;
int prime[maxn];
bool isprime[maxn];

int prime_cnt(int n)
    {
        int p=0;
        memset(isprime,true,sizeof(isprime));
        isprime[0]=false;
        isprime[1]=false;
        for (int i=2;i<=n;i++)
            {
                if(isprime[i])
                    {
                        prime[p++]=i;
                        for (int j=2*i;j<=n;j+=i)
                            isprime[j]=false;
                    }
            }
        return p;
    }
int main()
    {
        int n;
        while (cin>>n)
            {
                cout<<prime_cnt(n)<<endl;
            }
        return 0;
    }

C++: #include<stdio.h>
#include<math.h>

int main(){
  int n;
  int i,j;
  while(scanf("%d", &n) != EOF){
    int m=1;
    for(i=2;i<=n;i++){
      for(j=2;j<n;j++){
	if(i%j == 0)
	  break;
	if(j==i-1 && i%j!=0)
	  m++;
      }
    }
    printf("%d\n",m);
  }
  return 0;
}

C++: #include <iostream>                                                                                                       
#include <vector>                                                                                                         
#include <list>                                                                                                           
                                                                                                                          
#define MAX 1000000                                                                                                       
                                                                                                                          
using namespace std;                                                                                                      
                                                                                                                          
int main() {                                                                                                              
  vector<int> prime_numbers;                                                                                              
  prime_numbers.push_back(2);                                                                                             
  prime_numbers.push_back(3);                                                                                             
  prime_numbers.push_back(5);                                                                                             
  prime_numbers.push_back(7);                                                                                             
                                                                                                                          
  list<int> search_list;                                                                                                  
  for (int i = 5; i < MAX; i++) {                                                                                         
    if (i % 2 != 0 && i % 3 != 0 && i % 5 != 0 && i % 7 != 0) {                                                           
      search_list.push_back(i);                                                                                           
    }                                                                                                                     
  }                                                                                                                       
  int h = search_list.front();                                                                                            
  while (h * h < search_list.back()) {                                                                                    
    prime_numbers.push_back(h);                                                                                           
    list<int>::iterator itr = search_list.begin();                                                                        
    while (itr != search_list.end()) {                                                                                    
      if (*itr % h == 0) {                                                                                                
        itr = search_list.erase(itr);                                                                                     
      } else {                                                                                                            
        itr++;                                                                                                            
      }                                                                                                                   
    }                                                                                                                     
    h = search_list.front();                                                                                              
  }                                                                                                                       
  for (list<int>::iterator itr = search_list.begin(); itr != search_list.end(); itr++) {                                  
    prime_numbers.push_back(*itr);                                                                                        
  }                                                                                                                       
                                                                                                                          
  int n;                                                                                                                  
  while (cin >> n) {                                                                                                      
    int count = 0;                                                                                                        
    for (vector<int>::iterator itr = prime_numbers.begin(); itr != prime_numbers.end(); itr++) {                          
      if (*itr >= n) break;                                                                                               
      count++;                                                                                                            
    }                                                                                                                     
    cout << count << endl;                                                                                                
  }                                                                                                                       
                                                                                                                          
  return 0;                                                                                                               
}