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 and macros
#define debug(x) cout<<#x<<": "<<x<<endl
#define rep(i, a, b) for(int i=a; i < b;i++)
#include <algorithm>
#include <iostream>
#include <string>
#include <utility>
#include <vector>
#include <deque>
#include <set>
using namespace std;
// }}}

// {{{ io
void newline() {cout << endl;}
template <typename T>
void display(T input){cout << input;}
template <typename T>
void put(T input){display(input); newline();}
  // }}}

const int n_max = 100000;
const int prime_number_max = 200270;
const int p_max = 100;
vector<int> prime_numbers;
int n, p;

//テ」ツつィテ」ツδゥテ」ツδ暗」ツつケテ」ツδ?」ツδ催」ツつケテ」ツ?ョテァツッツゥ
void reserve_prime_numbers(){
      // テヲツ閉エテヲツ閉ーテ」ツ?ョテ」ツ?オテ」ツつ凝」ツ??」ツつ津、ツスツ愿ヲツ按静」ツ?凖」ツつ凝」ツ??・ツ按敕ヲツ慊淌ィツィツュテ・ツョツ?
   const int sievesize = prime_number_max;
   std::vector<int> sieve(prime_number_max, 1);

      // 1 テ」ツδ禿」ツδε」ツδ暗」ツ?ョテ、ツスツ催ァツスツョテ」ツつ津ヲツ、ツ愿ァツエツ「テ」ツ?凖」ツつ?
   for (int i = 2; i * i < sievesize; i++)
      if (sieve[i])
         for (int j = i + i; j < sievesize; j += i)
            sieve[j] = 0;

      // テヲツ慊?・ツセツ古」ツ?ォテ」ツ??ィツィツュテ・ツョツ堙」ツ?陛」ツつ古」ツつ凝・ツ?、テ」ツつ津・ツ?コテ・ツ環崚」ツ?凖」ツつ?
   for (int j = 2; j < sievesize; j++)
      if (sieve[j])
        prime_numbers.push_back(j);
}

int solve(){
  vector<int> prime_numbers_sum;
  for(int i=0; i<10000; i++){
    for(int l=i; l<10000; l++){
      int sum = prime_numbers[i] + prime_numbers[l];
      if(sum >= n){
        prime_numbers_sum.push_back(sum);
      }
    }
  }
  sort(prime_numbers_sum.begin(), prime_numbers_sum.end());
  return prime_numbers_sum[p-1];
}

int main(){
  prime_numbers.reserve(prime_number_max);
  reserve_prime_numbers();
  cin >> n >> p;
  put(solve());
}

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

bool prime[200001];
int n,p;
int primebox[100000];

int main(void){
	memset(prime,true,sizeof(prime));
	prime[0]=prime[1]=false;
	for(int i=2;i<=200000;i++){
		if(prime[i]){
			for(int j=i*2;j<=200000;j+=i){
				prime[j]=false;
			}
		}
	}
	int cnt=0;
	for(int i=2;i<=200000;i++){
		if(prime[i])primebox[cnt++]=i;
	}
	while(1){
		scanf("%d %d",&n,&p);
		if(n+p==-2)break;
		int l=0;
		while(primebox[l]<=n)l++;
		vector<int> v;
		for(int i=l;i<=min(l+100,cnt-1);i++){
			for(int j=i;j<=min(cnt-1,l+100);j++){
				v.push_back(primebox[i]+primebox[j]);
			}
		}
		sort(v.begin(),v.end());
		printf("%d\n",v[p-1]);
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define pb         push_back

const int INF = 1000000000;
const int MOD = 1000000007;
const int MAX = 10000000;

bool prime[MAX];

void era(int n){
	for(int i=0; i<n; i++){
		if(i % 2 == 0){
			prime[i] = false;
		}else{
			prime[i] = true;
		}
	}
	prime[0] = prime[1] = false;
	prime[2] = true;

	for(int i=3; i*i <=n; i+=2){
		if(prime[i] == true){
			for(int j=2; i*j <= n; j++){
				prime[i*j] = false;
			}
		}
	}
}

int main(void) {
	//ios_base::sync_with_stdio(false);
	//cin.tie(0);
	era(MAX-1);

	while(1){
		int n, p;
		cin >> n >> p;
		if(n == -1 && p == -1) break;
		vector<int> plist;
		vector<int> M;
		
		for(int i=n+1; ; i++){
			if(prime[i]){
				plist.push_back(i);
			}
			if(plist.size() > 200) break;
		}

		for(int i=0; i<plist.size(); i++){
			for(int j=i; j<plist.size(); j++){
				M.push_back(plist[i] + plist[j]);
			}
		}
		sort(M.begin(), M.end());

		cout << M[p-1] << endl;
	}

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define rep(i,n) for(int i=0;i<n;i++)
using vi=vector<int>;
using vvi=vector<vi>;
using pii=pair<int,int>;
using vlai=valarray<int>;

#include <bits/stdc++.h>
using namespace std;
using vi=vector<int>;
using vvi=vector<vi>;
using vs=vector<string>;
using msi=map<string,int>;
#define rep(i,n) for(int i=0;i<n;i++)
#define range(i,s,n) for(int i=s;i<n;i++)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
class Eratosthenes{
  public:
    int n, sqlim;
    vector<bool> prime;
    Eratosthenes(int N):n(N+1){
        sqlim=(int)ceil(sqrt(n));
        prime=vector<bool>(n,1); prime[0]=prime[1]=0;
        calc(); }

    void calc(){for(int i=2;i<=sqlim;i++) if(prime[i]) for(int j=i*i;j<=n;j+=i) prime[j]=0;}
    vi primeArray(int s=0, int l=10000){vi ret; for(int i=s;ret.size()!=l;i++) if(prime[i]) ret.push_back(i); return ret;}
};

int main(void){
    int n,p,l=100;
    Eratosthenes e(110000);
    while(cin>>n>>p,n!=-1){
        auto v=e.primeArray(n+1,l);
        vi res;
        rep(i,l)range(j,i,l)res.push_back(v[i]+v[j]);
        sort(all(res));
        cout<<res[p-1]<<endl;
    }
}