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 <iostream>
#include <cstdlib>
#include <string>
#include <cmath>
#include <algorithm>
using namespace std;
#define N 100000

int main(){
        int n, p, sosuu[100],count=0,sum[10000];
        string keymoji;

        cin >> n >> p;
        while(n != -1 && p != -1){
                int i=n;
                count = 0;
                int tmp=sqrt(n);
                if(i<2)i=2;
                for(; count<p; i++){
                        int tmp;
                        if(i==2){
                                sosuu[count]=i;
                                count++;
                                continue;
                        }
                int m=sqrt(i);
                        for(int j=2;j<i;j++){
                                if((tmp=i%j) == 0)break;
                        }
                        if(tmp != 0){
                                sosuu[count]=i;
                                count++; 
                        }
                        
                }
                count =0;
                for(i=0; i<p; i++){
                        for(int j=i; j<p; j++){
                                sum[count]=sosuu[i]+sosuu[j];
                                count++;
                        }
                }

                sort(sum, sum+count);
                cout << sum[p-1] << endl;
                cin >> n >> p;

        }

}

C++: #include <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
using namespace std;
#define INF 100000000
#define NUM 1000000

typedef long long ll;
const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};

int n, p;

bool prime[NUM];

int main(void) {
    for (int i = 0; i < NUM; i++) prime[i] = true;
    prime[0] = prime[1] = false;
    for (int i = 2; i * i <= NUM; i++) {
        if (prime[i]) {
            for (int j = 2; i * j <= NUM; j++) {
                prime[i*j] = false;
            }
        }
    }
    // 素数数列
    vector<int> P;
    for (int i = 2; i < NUM; i++) {
        if (prime[i]) P.push_back(i);
    }
//    for (int i = 0; i < 100; i++) {
//        if (prime[i]) cout << i << endl;
//    }
    while (cin >> n >> p) {
        if (n == -1 && p == -1) break;
        // nより大きい素数を挙げていく
        int index = 0;
        for (int i = 0; i < P.size(); i++) {
            if (n < P[i]) {
                index = i;
                break;
            }
        }
        vector<int> Q;
        for (int i = 0; i <= p; i++) {
            for (int j = i; j <= p; j++) {
                Q.push_back(P[index+i] + P[index+j]);
            }
        }
        sort(Q.begin(), Q.end());
        cout << Q[p-1] << endl;
    }
    return 0;
}

C++: #include <stdio.h>
#include <math.h>
#include <string.h>
#define MAXNUM 200274

int main(void){
	int n, p, i, j, count1, count2, flag[MAXNUM + 1], tmp[MAXNUM + 1];
	for(i = 0;i <= MAXNUM;i++)
		flag[i] = 1;
	flag[0] = flag[1] = 0;
	for(i = 2;i <= sqrt((double)MAXNUM);i++){
		for(j = 2 * i;j <= MAXNUM;j+=i)
			flag[j] = 0;
	}
	while(1){
		scanf("%d%d",&n,&p);
		if(n == -1 && p == -1)
			break;
		count1 = 0;
		memset(tmp,0,sizeof(tmp));
		for(i = n + 1;count1 < p;i++){
			if(flag[i]){
				count1++;
				count2 = 0;
				for(j = i;count2 < p;j++){
					if(flag[j]){
						count2++;
						tmp[i + j]++;
					}
				}
			}
		}
		count1 = 0;
		for(i = n + 1;count1 < p;i++){
			if(tmp[i]){
				count1 += tmp[i];;
			}
		}
		printf("%d\n",i - 1);
	}
	return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<string>
#include<functional>
#include<queue>
#include<algorithm>
#include<complex>
#include<cstdlib>
#include<cctype>

#define REP(i,n) for(int i = 0;i < (n);i++)
#define PB push_back
#define MP make_pair
#define FI first
#define SE second
#define SHOW1d(v,n) {for(int i = 0;i < (n);i++)cout << v[i] << ' ';cout << endl << endl;}
#define SHOW2d(v,i,j) {for(int a = 0;a < i;a++){for(int b = 0;b < j;b++)cout << v[a][b] << ' ';cout << endl;}cout << endl;}
#define ALL(v) v.begin(),v.end()

using namespace std;

typedef long long ll;
typedef vector<int> iv;
typedef vector<iv> iiv;
typedef vector<string> sv;

bool isprime(int n)
{
	if(n==1)return false;
	
	for(int i = 2;i*i <= n;i++)
	{
		if(n%i == 0)return false;
	}
	return true;
}

int main()
{
	int n,p;
	
	while(cin>>n>>p,n!=-1)
	{
		int _cou=0;
		int num = n+1;
		iv v1;
		iv v;
		while(_cou<p)
		{
			if(isprime(num)==true)
			{
				v1.PB(num);
				_cou++;
			}
			num++;
		}
		
		REP(i,p)for(int j = i;j < p;j++)
		{
			v.PB(v1[i]+v1[j]);
		}
		
		sort(ALL(v));
		
		cout << v[p-1] << endl;
		
	}
		
	return 0;
}