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 <stdio.h>
#include <algorithm>
#include <vector>
#include <queue>
#include <numeric>
#include <string>
#include <string.h>
#include <map>
#include <set>
#include <functional>
#include <complex>

using namespace std;

const int INF = (1<<30) - 1;

const int P_MAX = 2000000;
vector<bool> is_prime(P_MAX, true);
vector<int> primes;
void sieve(){
    for(int i=2; i<P_MAX; i++){
        if(is_prime[i]){
            primes.push_back(i);
            for(int j=i*2; j<P_MAX; j+=i)
                is_prime[j] = false;
        }
    }
}

int main(){
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    
    sieve();
    
    int N, P;
    while(cin>>N>>P, (N>=0 && P>=0)){
        auto it = upper_bound(primes.begin(), primes.end(), N);
        vector<int> vec;
        for(auto i=it; i<it+P; i++){
            for(auto j=i; j<it+P; j++){
                vec.push_back((*i)+(*j));
            }
        }
        sort(vec.begin(), vec.end());
        cout << vec[P-1] << endl;
    }
    
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for(int i=0;i<(n);i++)
const int MAXN = 2*1e5;
vector<int> pri(2*(int)1e5,true);

void prim(){
	pri[1] = false;
	for(int i=2;i*i<MAXN;i++){
		if(pri[i])
			for(int j=2*i;j<MAXN;j+=i)
				if(pri[j])pri[j] = false;
	}
}
int main(){
	int n,p;
	prim();
	while(cin >>n>>p,n!=-1){
		vector<int> twop;
		int limitt = n+p*10;
		for(int i=n+1;i<limitt;i++){
			if(pri[i])
				for(int j=i;j<limitt;j++){
					if(pri[j])twop.push_back(i+j);
				}
		}
		sort(twop.begin(),twop.end());
		cout << twop[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 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());
  return prime_numbers_sum[p-1];
}

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

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

const int LIM = 3000000;

char isprime[LIM];
int primes[LIM];
int PRIME_LIM = 0;

void eratosthenes() {
    fill(isprime, isprime + LIM, 1);
    isprime[0] = isprime[1] = 0;

    for(int x = 2; x * x < LIM; ++x) {
        if(!isprime[x]) continue;

        for(int y = x * x; y < LIM; y += x) {
            isprime[y] = 0;
        }
    }

    for(int x = 0; x < LIM; ++x) {
        if(isprime[x]) {
            primes[PRIME_LIM++] = x;
        }
    }
}

int solve(int N, int P) {
    vector<int> mtseq;
    int* ub = upper_bound(primes, primes + PRIME_LIM, N);

    for(int s = 0; s <= P; ++s) {
        for(int j = 0; j <= s; ++j) {
            int m = ub[s] + ub[j];
            mtseq.push_back(m);
        }
    }

    sort(begin(mtseq), end(mtseq));

    return mtseq[P - 1];
}

int main() {
    eratosthenes();
    int N, P;
    while(true) {
        cin >> N >> P;
        if(N == -1 && P == -1) break;
        cout << solve(N, P) << endl;
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
int isPrime(int n){
    for(int i=2;i*i<=n;i++) if(n%i==0) return 0;
    return 1;
}
int main(){
    int isp[200000]={};
    for(int i=2;i<200000;i++) isp[i]=isPrime(i);
    int n,p;
    while(cin>>n>>p){
        if(n==-1 && p==-1) break;
        int k=n;
        int c=0;
        int tmp[100]={};
        while(c<100){
            k++;
            if(isp[k]==1){
                tmp[c]=k;
                c++;
            }
        }
        vector<int> vec;
        for(int i=0;i<100;i++){
            for(int j=i;j<100;j++){
                vec.push_back(tmp[i]+tmp[j]);
            }
        }
        sort(vec.begin(),vec.end());
        cout<<vec[p-1]<<endl;
    }
    
    return 0;
}