Go: package main

import (
  "fmt"
  "math"
)

func main() {
  const N = 1000000
  var temp [N+1]bool
  for i:=0; i<N+1; i++ {
    temp[i] = true
  }
  temp[0] = false
  temp[1] = false
  for i:=2; i<int(math.Ceil(math.Sqrt(float64(N+1)))); i++{
    if (temp[i]){
      for j:=i*2; j<N+1; j+=i{
        temp[j] =false
      }
    }
  }
  var a int
  var b int
  for _, err := fmt.Scan(&a); err == nil; _, err = fmt.Scan(&a) {
    b = 0
    for i:=0; i<=a; i++{
      if temp[i] {
        b++
      }
    }
    fmt.Println(b)
  }
}

C++: 
#include<stdio.h>
int main()
{
    int a,N,M,sum=0,i,j,count=0,flag=0;
    while (scanf ("%d",&M)!=EOF )
        {
            for(i=2;i<=M;i++)
            {
                flag=0;

                if(i>2)
                {
                    for(j=2;j<i;j++)
                    {
                        if(i%j==0)
                        {
                            flag=1;
                            break;
                        }
                    }
                    if(flag==0)
                    {
                        count++;

                    }
                }

            }
                  printf("%d\n",count);
                  count=0;
        }

    return 0;
}

C++: #include<iostream>
using namespace std;

int main()
{
	bool is_prime[100000]:
	
	is_prime[0]=is_prime[1]=false;
	for(int i=2;i<1000000;i<i++){
		is_prime[i]=true;
	}
	
	for(int i=2;i*i<1000000;i++){
		if(is_prime[i]){
			for(int j=i*i;j<1000000;j+=i){
				is_primej]=false;
			}
		}
	}
	
	int n_prime[1000000];
	
	int cnt=0;
	for(int i=0;i<1000000;i++){
		if(is_prime[i]){
			cnt++;
		}
		
		n_prime[i]=cnt;
	}
	
	while(true){
		int n;
		cin>>n;
		if(cin.eof())
			break;
		
		cout<<n_prime[n]<<endl;
	}
	
	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define LOG(...) fprintf(stderr, __VA_ARGS__)
//#define LOG(...)
#define FOR(i, a, b) for(int i=(int)(a); i<(int)(b); ++i)
#define REP(i, n) for(int i=0; i<(int)(n); ++i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define EXIST(s, e) ((s).find(e)!=(s).end())
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort(RALL(c))
#define SQ(n) (n) * (n)

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int MAX_VALUE = 100007;
bool prime[MAX_VALUE];

int main() {
  vi primes;
  FOR(i, 2, MAX_VALUE){
    if(prime[i]) continue;
    primes.push_back(i);
    for(int j = i * 2; j<MAX_VALUE; j+=i)
      prime[j]=true;
  }

  int n;
  while(cin >> n) {
    REP(i, primes.size()){
      if(primes[i]-1 >= n) {
        cout << i << endl;
        break;
      }
    }
  }
}

C++: #include<cstdio>
#include<iostream>
#include<algorithm>
#include<vector>
#include<set>
#include<string>
#include<functional>
#include<queue>
#include<stack>
#include<math.h>
#define INF 999999

using namespace std;

typedef long long ll;

vector<int>primenumber;
int d[10500000];

int main()
{
	int n;
	
	primenumber.push_back(2);
	d[2] = 1;

	int maxn = 0;

	while (cin >> n) {
		if (maxn<n) {
			for (int i = max(maxn+1,3); i <= n; i++) {
				int ope = 1;
				for (int j = 0; j < primenumber.size(); j++) {
					if (primenumber[j] * primenumber[j] > i)break;
					if (i%primenumber[j] == 0) {
						ope = 0;
						break;
					}
				}
				if (ope == 1)primenumber.push_back(i);
				d[i] = primenumber.size();
			}
			maxn = n;
		}
		cout << d[n] << endl;
	}
	
	for (int i = 0; i < primenumber.size(); i++) {
		cout << primenumber[i] << endl;
	}

	return 0;
}

C++: #include <iostream>
#include <math.h>
using namespace std;

int main(){
  
  int n;

  while(cin >> n){
    bool Prime[1000000] = {};
    int i,j;
  
    for(i = 2; i <= sqrt(n) ; i++){
      if(Prime[i] == false){
        
	for(j = 2; i*j <= n ; j++){
	  Prime[i*j] = true;
	}
      }
    }
    int count = 0;
    for(i = 2 ; i <= n ; i++){
      if(Prime[i] == false){
	count++;
      }
    }
    cout << count << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <sstream>
#include <vector>
#include <algorithm>
#include <string>
#include <functional>
#include <numeric>
#include <ctype.h>
#include <cstdlib>
#include <string.h>
#include <cmath>
#include <cstdio>





using namespace std;

bool isPrime(int num);

int main()
{
	int count = 0;
	/*int m = 2, n = 0, num;

	cin >> num;

	int *data = new int[num + 1];
	int *result = new int[num + 1];

	data[0] = 0;
	data[1] = 0;

	do
	{
		for (i = 2 * m; i < num + 1; i += m)
		{

		}
	}
	while
	{

	}*/
	const int N = 9999999;
	int n;
	std::vector<bool> isPrime(N + 1, true);    // ?´???°????????°?????¨??¨ON???

	while (cin >> n)
	{
		count = 0;
		for (int i = 2; i <= n; ++i) {
			if (isPrime[i])
			{
				count++;

				for (int k = i + i; k <= n; k += i)
					isPrime[k] = false;      // ?´???°????????°????´???°????????°?????¨???OFF???
			}
		}

		cout << count << endl;
	}
	
	return 0;






	
}

C++: #include <iostream>
using namespace std;

int main(){
	bool b[1000000] = {};
	for(int i = 2; i < 1000000; i++){
		b[i] = true;
	}
	for(int i = 2; i < 1000; i++){
		if(b[i]){
			for(int j = i * i; j < 1000000; j += i){
				b[j] = false;
			}
		}
	}

	int n, count = 0;
	cin >> n;
	for(int i = 0; i <= n; i++){
		if(b[i]){
			count ++;
		}
	}
	cout << count << endl;
	return 0;
}

C++: #include<stdio.h>
int main(void)
{
	int i=0,j=0;
	int n=0;
	int count=0;
	int kioku[200000]={0};
	int flg=0;
	while (scanf("%d",&n)!=EOF)
	{
		count=0;
		if (n>=2)
		{
			kioku[0]=2;
			count++;
		}
		for (i=3;i<=n;i+=2)
		{
			for (j=0;j<count;j++)
			{
				if (i%kioku[j]==0)
				{
					flg=1;
					break;
				}
			}
			if (flg==1)
			{
				flg=0;
			}
			else
			{
				kioku[count]=i;
				count++;
			}
		}
		printf("%d\n",count);
	}
	return 0;
}

C++: #include<stdio.h>



int main(){
	int n,i,j;
	bool c[1000];
	int data[1000];
	int count;
	int premaxin=1;


	for(i=0;i<1000;i++){
		c[i]=1;
		data[i]=0;
	}
	c[0]=c[1]=0;

	while(scanf("%d",&n)!=EOF){

		if(premaxin<n){
			for(i=0;i<=n;i++){
				if(c[i]==1){
					if(premaxin>i){
						j=premaxin;
					}else{
						j=i+1;
					}
					for(;j<=n;j++){
						if(j%i==0){
							c[j]=0;
						}
					}
				}
			}

			count=data[premaxin];
			for(i=premaxin+1;i<=n;i++){

				if(c[i]==1){
					count++;
				}
				data[i]=count;
			}
		}

		printf("%d\n",data[n]);
	}
	return 0;
}

C++: #include <stdio.h>

int main(){
	int sosuu[] = { 2, 3, 5 }, i, x, y = 3,n=0,z;
	
	while (scanf("%d", &n)!=EOF){
		z = 0; 
		for (i = 3; i < n + 1; i += 2){
			for (x = 0; x < y; x++){
				if (i % sosuu[x] == 0)break;
				if (x + 1 == y){ sosuu[y] = i, y++;}
			}
		}
		for (i = 0; i < y; i++){ if (sosuu[i] > n)break; z++; }
		printf("%d\n", z);
	}
	return 0;
}

C++: #include <iostream>
using namespace std;


int main(){
	int number,cnt=0;
	cin>>number;
	int* arr = new int[number+1];
	for (int i = 1; i <= number; i+=2)
	{
		arr[i-1]=0;
		arr[i]=1;
	}
	for (int i = 3; i < sqrt(number); i+=2)
		if (arr[i])
			for (int j = i+i; j <=number; j+=i)
				arr[j]=0;
	arr[2]=1;arr[1]=0;
	for (int i = 0; i < number; i++)
		if (arr[i])
			++cnt;
	cout<<cnt;
}

C++: #include <iostream>
#include <cmath>
#include <algorithm>
#include <map>
#include <string>
#include <vector>
#define FOR(i, a, b)  for(int i=a; i<b; ++i)
#define rFOR(i, a, b) for(int i=a-1; i>=b; --i)
#define REP(i, n) for(int i=0; i<n; ++i)
#define rREP(i, n) for(int i=n-1; i>=0; --i)
#define all(a)  a.begin(), a.end()
using namespace std;

int main(){
  int n;
  while(cin >> n){
    int ans = 1;
    for(int i = 3; i<=n; i+=2){
      bool isSosu = true;
      for(int j=3; j <= floor(sqrt(i)); j++){
        if(i%j == 0){
          isSosu = false;
          break;
        }
      }
      if(isSosu){
        ans++;
      }
    }
    cout << ans << endl;;
  }
  return 0;
}