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 prime_number_max = 50;
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<prime_numbers.size(); i++){
    for(int l=i; l<prime_numbers.size(); 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());
  for(auto a: prime_numbers_sum){put(a);}
  return prime_numbers_sum[p-1];
}

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

C++: #include <iostream>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <string>
#include <sstream>
#include <numeric>
#define rep(i, j) for(int i = 0; i < j; i++)
#define all(i) i.begin(), i.end()
using namespace std;
vector<bool> era(1000010, true);
void makePrimeTable(int n)
{
	era[0] = false; era[1] = false;
	for (int i = 2; i <= n; i++)
	{
		if (era[i]) { for (int j = i * 2; j <= n; j += i) { era[j] = 0; } }
	}
}
int main()
{
	makePrimeTable(200000);
	int N, P; while (cin >> N >> P && N != -1)
	{
		vector<int> dat(0);
		vector<int> prm(0);
		while (1)
		{
			N++;
			if (era[N]) { prm.push_back(N);}
			if (prm.size() == P) { break; }
		}
		for (int i = 0; i < P; i++) for (int j = i; j < P; j++) { dat.push_back(prm[i] + prm[j]); }
		sort(all(dat)); 
		printf("%d\n", dat[P - 1]);
	}
	return 0;
}

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

using namespace std;

const int MAX_N = 100000;
const int MAX_P = 100;
const int MAX_PRIME = (MAX_N+MAX_P)*2+100;

int prime[MAX_N];
int n_prime;

void init_prime() {
  prime[0] = 2;
  n_prime = 1;
   for (int i=3;i<MAX_PRIME;i++) {
    if (i%2 == 0) continue;
    bool ok = true;
    for (int j=3;j<=sqrt(i);j+=2) {
      if (i%j == 0) {
        ok = false;
        break;
      }
    }
    if (ok) prime[n_prime++] = i;
  }
}

int main() {
  init_prime();
  while (true) {
    int N, P;
    scanf("%d %d", &N, &P);
    if (N == -1 && P == -1) break;
    const int* p = upper_bound(prime, prime+n_prime, N);
    vector<int> t;
    for (int i=0;i<P;i++) {
      for (int j=i;j<P;j++) t.push_back(p[i]+p[j]);
    }
    sort(t.begin(), t.end());
    printf("%d\n", t[P-1]);
  }
  return 0;
}

C++: #include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int psize = 1000000;
    vector<int>num(psize+1);//prime is 0
    num[0] = num[1] = 1;
    for(int i = 2;i * i <= psize;i++){
        if(num[i])continue;
        for(int j = i * 2;j <= psize;j += i){
            num[j] = 1;
        }
    }
    vector<int>prime;
    rep(i,0,psize+1){
        if(!num[i])prime.push_back(i);
    }
    
    int N,P;
    cin >> N >> P;
    while(N != -1){
        auto itr = upper_bound(prime.begin(), prime.end(), N);
        auto itr2 = itr;
        int d = distance(prime.begin(), itr);
        multiset<int>st;
        /*          
        rep(i,0,100){
            rep(j,0,100){
                st.insert(*itr + *itr2);
                itr2++;
            }
            itr++;
        }
                  */
        rep(i,0,100){
            rep(j,i,100){
                st.insert(prime[i + d] + prime[j + d]);
            }
        }
        //sort(num.begin(), num.end()); 
        //cout << num[P-1] << endl;
        auto itr3 = st.begin();
        rep(i,0,P-1){
            itr3++;
        }
        cout << *itr3 << endl;
        cin >> N >> P;
    }
    
}