Go: package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"sort"
	"strconv"
	"strings"
)

func main() {
	io := NewIo()
	defer io.Flush()
	for {
		n, p := io.NextInt(), io.NextInt()
		if n == -1 {
			break
		}
		isPrime := SieveOpt(200000)
		prime := make([]int, p)
		cnt := 0
		if n < 2 {
			prime[0] = 2
			cnt++
		}
		for i := (n + 1) / 2; i < len(isPrime) && cnt < p; i++ {
			if isPrime[i] == true {
				prime[cnt] = 2*i + 1
				cnt++
			}
		}
		comb := make([]int, 0, p*p)
		for i := 0; i < p; i++ {
			for j := i; j < p; j++ {
				comb = append(comb, prime[i]+prime[j])
			}
		}
		sort.Ints(comb)
		io.Println(comb[p-1])
	}
}

func SieveOpt(x int) []bool {
	flags := make([]bool, x/2) // flags[i] := 2*j+1 is prime
	for i := 1; i < x/2; i++ {
		flags[i] = true
	}
	sqrtXi := int(math.Ceil(math.Sqrt(float64(x)))) / 2
	for i := 1; i < sqrtXi; i ++ {
		if !flags[i] {
			continue
		}
		for j := 2 * i * (i + 1); j < x/2; j += 2*i + 1 {
			flags[j] = false
		}
	}
	return flags
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string> 
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

int min_prime(int n);
int isprime(int n);

int main()
{
	int n, p;
	while(1){
		cin >> n >> p;
		if(n == -1 && p == -1) break;
		int prime_array[1000] = {0}, sum_array[10000] = {0};
		if(isprime(n)) prime_array[0] = n;
		else prime_array[0] = min_prime(n);
		for(int i = 0; i < 100; i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < p; i++){
			for(int j = i; j < p; j++){
				sum_array[k] = prime_array[i] + prime_array[j];
				k++;
			}
		}
		sort(sum_array, sum_array+k);
		cout << sum_array[p - 1] << endl;
	}
	return 0;
}

int min_prime(int n)
{
	int i = 1;
	while(1){
		if(isprime(n + i)) return n + i;
		else i++;
	}
}

int isprime(int n)
{
	int ans;
	if(n == 0 || n == 1) ans = 0;
	else if(n == 2) ans = 1;
	else {
		for(int i = 2; i < n; i++){
			if(i * i > n) ans = 1;
			else if(n % i == 0){
				ans = 0;
				break;
			}
		}
	}
	return ans;
}

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

const int N = 5000000;
bool prime[N];
int main() {
    for (int i=0; i<N; ++i) prime[i] = 1;
    prime[0] = prime[1] = 0;
    for (int i=2; i<N; ++i) {
        if (prime[i])
            for (int j=i*2; j<N; j+=i)
                prime[j] = 0;
    }
    vector<int> v;
    for (int i=0; i<N; ++i) if (prime[i]) v.push_back(i);
    
    int n, p;
    while(cin>>n>>p, n!=-1) {
        int a = upper_bound(v.begin(), v.end(), n) - v.begin();
        vector<int> ans;
        for (int i=a; i<a+100; ++i) {
            for (int j=a; j<=i; ++j) {
                ans.push_back(v[i]+v[j]);
            }
        }
        sort(ans.begin(), ans.end());
        //for (int i=0; i<100; ++i) cout << ans[i] << " ";cout <<endl;
        cout << ans[p-1] << endl;
    }
}

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

vector<int> seive(int n){
  vector<bool> is_prime(n + 10, true);
  vector<int> res;
  is_prime[0] = is_prime[1] = false;
  for (int i = 2; i <= n; i++) {
    if(is_prime[i])res.push_back(i);
    for (int j = 2*i; j <= n; j+=i) is_prime[j] = false;
  }
  return res;
}

int main(){
  int n, m;
  vector<int> prime = seive(5e5 + 10);
  while(std::cin >> n >> m, n != -1 or m != -1){
    int a = upper_bound(prime.begin(), prime.end(), n) - prime.begin();
    multiset<int> ans;
    for (int i = 0; i < 108; i++) {
      for (int j = i; j < 108; j++) {
        ans.insert(prime[a + i] + prime[a + j]);
      }
    }
    auto x = ans.begin();
    for (int i = 0; i < m - 1; i++, x++);
    std::cout << *x << std::endl;
  }
  return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define Max 500000
vector<int> prim;
vector<bool> res(Max+1,true);
void aris(int n){
res[0]=res[1]=false;
	for(int i=2;i<=n;i++){
		if(res[i]){
			prim.push_back(i);
			int k=2;
			while(i*k<=n){
			res[i*k]=false;
			k++;
			}
		}
	}
	return ;
}

int main(){
int n,p;

aris(Max);
while(1){
	cin>>n>>p;
	if(n==-1)break;
	vector<int> tmp,ans;
auto now =upper_bound(prim.begin(),prim.end(),n);
for(int i=0;i<=p;i++){
tmp.push_back(*now);
	for(int j=0;j<=i;j++)ans.push_back(tmp[i]+tmp[j]);
now++;
//if(ans.size()>p)break;
}
sort(ans.begin(),ans.end());
cout<<ans[p-1]<<endl;

		}
return 0;
}

C++: #include<stdio.h>
int prime[1300001];

void isprime(void){
    int i,j,n,c;

    for(i = 4;i<1300001;i += 2)prime[i] = 1;

    for (i = 3;i * i <= 1300001;i += 2){
        if (prime[i] == 0){
            for (j = i + i; j <= 1300001; j += i){
                prime[j] = 1;
            }
        }
    }
}

int main(void){
    int n,i,a=0;
    int flag,p,j,k;
    isprime();
    
    while (scanf("%d%d",&n,&p),n==-1&&p==-1){
a=0;
flag=0;
        for(i = (n+1)*2;;i++){
for(j = n+1;j < i;j++){
 for(k = j;j+k <= i;k++){
  if(j+k == i){
   if(prime[j]*prime[k]){
    a++;
    if(a==p){
     printf("%d\n",i);
flag=1;
break;
    }
   }
  }
if(flag)break;
 }
if(flag)break;
}
if(flag)break;
        }
a:
    }
     
    return (0);
}