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<string>
#include<map>
#include<list>
#include<set>
#include<algorithm>
#include<limits.h>
#include<vector>
#define foreach(t,p) for(t::iterator it=p.begin();it!=p.end();p++)
using namespace std;
#define MAX 5000000

bool notp[MAX];

int main()
{
    notp[0]=true;
    notp[1]=true;
    for(unsigned int i = 2;i<MAX;i++)
        if(!notp[i]) for(unsigned int j=2*i;j<MAX;j+=i)
        {
            notp[j]=true;
        }
    vector<int> primes;
    for(int i =0;i<MAX;i++)
    {
        if(!notp[i]) primes.push_back(i);
        if(primes.size()>100100)break;
    }
    //for(int l=0;l<25;l++)cout << primes[l] << endl;
    int n,p;
    cin >> n >> p;
    int k;

    while(n!=-1 && p!=-1)
    {
        list<int> mnps;
        for(k=0;;k++) 
        {
            if (primes[k] > n ) break;
        }
        for(int i =0;i<100;i++)for(int j=i;j<100;j++)
            mnps.push_back(primes[i+k]+primes[j+k]);

        mnps.sort();
        list<int>::iterator mit = mnps.begin();
        for(int i =0;i<p-1;i++)++mit;
        cout << *mit << endl;
        cin >> n >> p;
    }
    return 0;
}

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<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());
  return prime_numbers_sum[p-1];
}

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

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

#define N_MAX 110000

void dump(vector<int>& v,int n){

	  for(int i=0; i<min(n,(int)v.size()); i++)
			cout << v[i] <<  " ";
	  cout << endl;
}

int main(){
	  
	  bool is_pri[N_MAX] = {false};
	  vector<int> pri; 

	  for(int i=2; i<N_MAX; i++) is_pri[i] = true;

	  for(int i=2; i<N_MAX; i++){
			if( is_pri[i] ) {
				  for(int j=2; j*i<N_MAX; j++)
						is_pri[i*j] = false;
				  pri.push_back(i);
			}
	  }

	  

	  int N,P;
	  while(cin >> N >> P){
			if(N==-1) break;

			int first = upper_bound(pri.begin(),pri.end(),N) - pri.begin();

			vector<int> ans(P,INT_MAX);
			for(int i=first; i<min(first+P,(int)pri.size()); i++){
				  for(int j=i; j<min(first+P,(int)pri.size()); j++){

						ans.push_back(pri[i]+pri[j]);
						sort(ans.begin(),ans.end());
						ans.pop_back();

						
				  }
			}
			cout << ans[P-1] << endl;
	  }

}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <string>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>

#define rep(i,j) REP((i), 0, (j))
#define REP(i,j,k) for(int i=(j);(i)<(k);++i)
#define between(a,x,b) ((a)<=(x)&&(x)<=(b))
using namespace std;
vector<int>prime(200000);
int main(){
  prime[0] = prime[1] = 1;
  REP(i, 2, 100000){
    if(prime[i] == 0){
      for(int j = 2*i; 2*j < 200000; j+=i) prime[j] = 1;
    }
  }
  int n, p;
  while(scanf("%d%d", &n, &p) && (n != -1 || p != -1)){
    vector<int>bprime;
    for(int i = n+1, c = 0; c < p; i++){
      if(prime[i] == 0){
	bprime.push_back(i);
	c++;
      }
    }

    vector<int>sum;
    rep(i, p) REP(j, i, p) sum.push_back(bprime[i] + bprime[j]);
    sort(sum.begin(), sum.end());
    printf("%d\n", sum[p-1]);
  }
  return 0;
}