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<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]==0&&prime[k]==0){
    a++;
    if(a==p){
     printf("%d\n",i);
flag=1;
break;
    }
   }
  }
if(flag)break;
 }
if(flag)break;
}
if(flag)break;
        }
    }
     
    return 0;
}

C++: #include <iostream>
#include <queue>
#include <cctype>
#include <stdio.h>
#include <map>
#include <string.h>
#include <algorithm>
#include <vector>

using namespace std;

int max(int a, int b);
int min(int a, int b);
int is_prime(int n);

int main(int argc, char const* argv[])
{
    int n,p;
    while (cin >> n >> p) 
    {
        if ( n==-1 && p==-1 ) { break; }
        vector<int> arr;

        //素数列を格納
        int count=0;
        int i=n+1;
        while ( count <  p ) 
        {
            if ( is_prime(i) ) 
            {
                //cout << "i = " << i << endl;
                arr.push_back(i);    
                count++;
            }
            i++;
        }

        //
        //for (int i = 0; i < p; i++) 
        //{
        //    cout << arr[i] << endl;
        //}

        //足した素数を格納
        vector<int> sum;
        for (int i = 0; i < p; i++) 
        {
            for (int j = i; j < p; j++) 
            {
                sum.push_back( arr[i] + arr[j] );
            }
        }
        sort(sum.begin(), sum.end());
        cout << sum[p-1] << endl;    
    }
    return 0;
}

int is_prime(int n)
{
    if (n ==1 || n== 0) 
    {
        return 0;
    }
    for (int i = 2; i*i <= n; i++) 
    {
        if (n % i == 0) 
        {
            return 0;
        }
    }
    return 1;

}


int max(int a, int b)
{
    if (a > b) 
    {
        return a;
    }
    else{
        return b;
    }
}
int min(int a, int b)
{
    if (a > b) 
    {
        return b;
    }
    else{
        return a;
    }
}

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<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<cassert>
#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<numeric>
#include<algorithm>
#include<bitset>
#include<complex>

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
#define mp make_pair

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cout << *i << " "; cout << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

bool prime[200000];

int main() {
	int i,j;
	for(i=0;i<200000;i++)prime[i]=true;
	prime[0]=prime[1]=false;
	for(i=0;i*i<200000;i++){
		if(!prime[i])continue;
		for(j=i*i;j<200000;j+=i){
			prime[j]=false;
		}
	}
	int n,p;
	while(1){
		cin>>n>>p;
		if(n==-1&&p==-1)break;
		vector<int> m;
		for(i=n+1;;i++){
			if(!prime[i])continue;
			for(j=i;;j++){
				if(!prime[j])continue;
				m.push_back(i+j);
				if(m.size()%p==0)break;
			}
			if(m.size()==p*p)break;
		}
		sort(m.begin(),m.end());
		cout<<m[p-1]<<endl;
	}
	return 0;
}