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<vector>
using namespace std;
int prime[200000];
bool is_prime[200000];
int sieve(int n);
vector<int> prime_prime;
int main(){
  sieve(200000);
  int i,j;
  int n,p;
  int count=0;
  while(cin>>n>>p){
    count=0;
    prime_prime.clear();
    if(n==-1 && p==-1)break;
    while(prime[count]<=n)count++;
    for(i=count;i<p+count;i++)
      for(j=i;j<p+count;j++)
	prime_prime.push_back(prime[i]+prime[j]);
    sort(prime_prime.begin(),prime_prime.end());
    //for(int i=0;i<num;i++)cout<<prime_prime[i]<<endl;    
    cout<<prime_prime[p-1]<<endl;
  }
  return 0;
}

int sieve(int n){
  int p = 0;
  int i,j;
  for(i = 0;i<=n;i++)is_prime[i] = true;
  is_prime[0] = is_prime[1] = false;
  for(i = 2;i<=n;i++){
    if(is_prime[i]){
      prime[p++]=i;
      for(j=2*i;j<=n;j+=i)is_prime[j]=false;
    }
  }
  return p;
}

C++: #define _USE_MATH_DEFINES
#include "bits/stdc++.h"
#define EPS 1e-10
using namespace std;
typedef long long llong;
#define N 105000
int main() {
	vector<bool>f(N, true);
	f[0] = false;
	f[1] = false;
	vector<int>prime;
	for (int i = 2; i <= sqrt(N); i++) {
		if (f[i]) {
			for (int j = 2; i*j < N; j++) {
				f[i*j] = false;
			}
		}
	}
	for (int i = 0; i < N; i++) {
		if (f[i]) {
			prime.push_back(i);
		}
	}

	int n, p;
	while (cin >> n >> p, p != -1) {
		auto it = upper_bound(prime.begin(), prime.end(), n);
		vector<int>ans(10000,100000000);

		for (int cnt = 0, i = 0; i < 100; i++) {
			for (int j = i; j < 100; j++) {
				ans[cnt++] = *(it + i) + *(it + j);
			}
		}
		sort(ans.begin(), ans.end());

		cout << ans[p - 1] << endl;


	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cmath>
#include<utility>
#include<set>
#include<complex>
#define vi vector<int>
#define vvi vector<vector<int> >
#define ll long long int
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vb vector<bool>
#define vc vector<char>
#define vs vector<string>
#define ld long double
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define CC puts("-------ok--------");
#define all(in) in.begin(), in.end()
#define bv vector<bool>
using namespace std;
typedef pair<int, int> PI;
#define MAX 1e7
int main(){
    int n,n2;
    vector<bool>check(MAX+1,true);
    vector<int>Primenumber(MAX+1,0); //Primearray
    int counter =0;                  //Primearray counter;
    for(int i = 2; i<MAX+1;i++){
        if(check[i]){
            for(int j = 2;i*j<MAX;j++)
                check[i*j] = false;//?´???°??????Primearray???????´??????????????????°?????¨???false???
            Primenumber[counter] = i;
            counter++;
        }
    }
    check[0]=false;
    check[1]=false;
    while(cin>>n>>n2,n+n2+2){
        /*n????????§???????´???°??§?§??????????????´???°??????n2?????????????????????*/
        vi v;
        for(int i=2*n;;i++){
            if(i<4)continue;
            //cout<<i<<endl;
            for(int j=i;(double)j>=(double)i/2;j--){
                if(check[j]&&check[i-j]&&i-j>n&&j>n)v.push_back(i);
                if(v.size()>n2)goto E;
            }
        }
    E: //ep(i,10)cout<<v[i]<<endl;
        cout<<v[n2-1]<<endl;
    }
}