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<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;
const int MAX_P = 100;

const int MAX_PNUM = MAX_N + MAX_P * 10;

/* typedef */

typedef vector<int> vi;

/* global variables */

bool primes[MAX_PNUM + 1];
vi pnums;

/* subroutines */

int calc_prime(int max_p) {
  memset(primes, true, sizeof(primes));
  primes[0] = primes[1] = false;

  for (int p = 2; p * p <= max_p; p++)
    if (primes[p])
      for (int q = p * p; q <= max_p; q += p) primes[q] = false;

  for (int p = 2; p <= max_p; p++)
    if (primes[p]) pnums.push_back(p);

  return pnums.size();
}

/* main */

int main() {
  calc_prime(MAX_PNUM);
  
  for (;;) {
    int n, p;
    cin >> n >> p;
    if (n < 0) break;

    vi::iterator pbgn = upper_bound(pnums.begin(), pnums.end(), n);
    vi::iterator pend = min(pbgn + 10 * p, pnums.end());
    
    vi sums;
    for (vi::iterator pit0 = pbgn; pit0 != pend; pit0++)
      for (vi::iterator pit1 = pit0; pit1 != pend; pit1++)
	sums.push_back(*pit0 + *pit1);
    sort(sums.begin(), sums.end());

    cout << sums[p - 1] << endl;
  }
  
  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<1000; i++){
    for(int l=i; l<1000; 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<iostream>
#include<string>
#include<vector>
#include<algorithm>
#define rep(X,Y) for(int (X)=0;(X)<(Y);++(X))
#define reps(i,j,k) for(int i=j;i<=k;i++)
#define pb push_back

typedef long long ll;
using namespace std;

#define MAX 300000
int prime[MAX];
vector<int> primes;

int main(){
	prime[0] = prime[1] = 1;
  for(int i=2;i<MAX;++i){
    if(prime[i])continue;
    primes.pb(i);
    for(int j=i*2;j<MAX;j+=i)
      prime[j]=1;
  }
  int n,p;
  while(cin >> n >> p){
	if(n<0)break;
	vector<int> v,w;
	for(int i=n+1;i<MAX&&v.size()<p;i++){
		if(!prime[i]) v.pb(i);
	}
	rep(i,v.size())reps(j,i,v.size()-1){
		w.pb(v[i]+v[j]);
	}
	sort(w.begin(),w.end());
	cout << w[p-1] << endl;
	//rep(i,w.size())cout << w[i] << endl;
  }
  //rep(i,10)cout<<primes[i]<<",";cout<<endl;
}

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

int main()
{
  const int MAX_P = 200000;
  static bool p[MAX_P];

  for (int i = 0; i < MAX_P; ++i)
    p[i] = true;
  p[0] = p[1] = false;
  for (int i = 2; i*i < MAX_P+1; ++i) {
    if (p[i]) {
      for (int j = i+i; j < MAX_P; j += i)
	p[j] = false;
    }
  }

  vector<int> prime;
  for (int i = 0; i < MAX_P; ++i) {
    if (p[i])
      prime.push_back(i);
  }

  int N, P;
  while (scanf("%d %d", &N, &P) != EOF) {
    if (N == -1 && P == -1)
      break;

    vector<int> ans;
    int p1 = 0, p2 = 0;
    for (vector<int>::iterator it = upper_bound(prime.begin(), prime.end(), N); it != prime.end() && p1 < P; ++it, ++p1) {
      p2 = 0;
      for (vector<int>::iterator jt = lower_bound(prime.begin(), prime.end(), *it); jt != prime.end() && p2 < P; ++jt, ++p2)
	ans.push_back((*it)+(*jt));
    }

    sort(ans.begin(), ans.end());
    printf("%d\n", ans[P-1]);
  }
  return 0;
}