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<vector>
#include<cmath>

using namespace std;

void eratosthenes(vector<int> &n){	
	n[1] = 1;
	for (int i = 2;i <= (120000/2); i++){
		n[i * 2] = 1;
	}
	int p = 3;
	while(p * p <= 120000){
		for (int i = p; i <= (120000/p); i++){
			n[i * p] = 1;
		}
		p++;
		while(n[p] == 1)p++;
	}
	return;
}

bool isPrime(int n){
	if (n < 2) return false;
	if (n == 2) return true;
	for (int i = 2; i <= sqrt(n) + 1; i++){
		if (n % i == 0) return false;
	}
	return true;
}
		
int main(){
	vector<int> era(120000);
	eratosthenes(era);
	vector<int> Primelist(120001);
	int index = 1;
	for (int i = 1; i <= era.size(); i++){
		if (era[i] == 0){
			Primelist[index] = i;
			index++;
		}
	}
	while(1){
		int n,p; cin >> n >> p;
		if (n + p == -2) break;
		index = 1;
		while(n >= Primelist[index]){
			index++;
		}
		
		vector<int> list(120000);
		for (int i = 1; i <= p; i++){
			for (int j = i; j <= p; j++){
				list[(i-1) * p + j] = Primelist[index + i - 1] + Primelist[index + j - 1];
			}
		}
		sort(list.begin(),list.end());
		index = 0;
		while(list[index] == 0){
			index++;
		}
		cout << list[index + p - 1] << endl;
		
	}

return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>
#include <set>
#include <vector>
#include <cstring>
#include <climits>
#include <queue>
#include <map>
#include <sstream>
using namespace std;

#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define EPS 1e-9

bool primes[101000];
void make_prime(){
	primes[0]=primes[1]=true;
	for(int i=2; i*i<=101000; i++)if( !primes[i] )
		for(int j=2*i; j<101000; j+=i)primes[j]=true;
}
int main(){
	int n,p;
	make_prime();
	while(scanf("%d%d",&n,&p),!(n==-1&&p==-1)){
		vector<int> tmp,e;
		for(int i=n+1,c=0; c<p; i++)if( !primes[i] ){
			c++;
			tmp.push_back(i);
		}
		for(int i=0; i<tmp.size(); i++){
			for(int j=i; j<tmp.size(); j++){
				e.push_back(tmp[i]+tmp[j]);
			}
		}
		/*
		rep(i,e.size()){
			printf("%d,",e[i]);
		}
		*/
		sort(e.begin(), e.end());
		printf("%d\n",e[p-1]);
	}
	return 0;
}

C++: #include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

bool is_prime(int n, int k = 2)
{
    if(n < k * k) { return true; }
    
    if(n % k == 0) { return false; }
    
    return is_prime(n, k + 1);
}

int main()
{
    vector<int> prime;
    
    for(int i = 2; i < 110000; i++)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
    
    int n, m;
    
    while(true)
    {
        scanf("%d", &n);
        scanf("%d", &m);
        
        if(n == -1 && m == -1) { break; }
        
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
        
        vector<int> c;
        
        for(int i = ptr; i < ptr + m; i++)
        {
            for(int j = i; j < ptr + m; j++)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
        
        sort(c.begin(), c.end());
        
        printf("%d", c[m - 1]);
    }
    
    return 0;
}

C++: m :#include<iostream>
#include<vector>
#include<cmath>
#include<algorithm>

using namespace std;

void eratosthenes(vector<int> &n){	
	n[0] = n[1] = 1;
	for (int i = 2;i <= 120000; i++){
		if (n[i] == 0){
			for (int j = 2; j <= (120000/i); j++){
				n[i * j] = 1;
			}

		}
	}
	return;
}

bool isPrime(int n){
	if (n < 2) return false;
	if (n == 2) return true;
	for (int i = 2; i <= sqrt(n) + 1; i++){
		if (n % i == 0) return false;
	}
	return true;
}
		
int main(){
	vector<int> era(120000);
	eratosthenes(era);
	vector<int> Primelist(120001);
	int index = 1;
	for (int i = 1; i <= era.size(); i++){
		if (era[i] == 0){
			Primelist[index] = i;
			index++;
		}
	}
	while(1){
		int n,p; cin >> n >> p;
		if (n + p == -2) break;
		index = 1;
		while(n >= Primelist[index]){
			index++;
		}
		
		vector<int> list(120000);
		for (int i = 1; i <= p; i++){
			for (int j = i; j <= p; j++){
				list[(i-1) * p + j] = Primelist[index + i - 1] + Primelist[index + j - 1];
			}
		}
		sort(list.begin(),list.end());
		index = 0;
		while(list[index] == 0){
			index++;
		}
		cout << list[index + p - 1] << endl;
		
	}

return 0;
}

C++: #include<iostream>
#include<cmath>
#include<algorithm>
#include<vector>

#define all(c) (c).begin(),(c).end()

using namespace std;

vector<int>p,v;
bool fg[101000];

int main(void){

  for(int i=2;i*i<101000;i++){
    if(!fg[i]){
      for(int j=i*i;j<101000;j+=i){
	fg[j]=true;
      }
    }
  }
  for(int i=2;i<101000;i++)
    if(!fg[i])p.push_back(i);

  int N,P;
  while(cin >> N >> P,0<=N && 0<=P){
    int b = upper_bound(all(p),N) - p.begin();
    
    v.clear();
    for(int i=b;i<p.size();i++){
      for(int j=i;j<p.size();j++){
	v.push_back(p[i]+p[j]);
      }
    }
    sort(all(v));
    cout << v[P-1] << endl;
  }
  
  return 0;
}