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<algorithm>
#include<vector>
using namespace std;

int main(){
  vector <int> result;
  int i,j,n,p,k,data[1100000],primenum[100000];
  for(i = 0; i < 1100000; i++){
    data[i]=0;
    primenum[i]=0;
  }

  for(i = 0; i < 100000; i++){
    primenum[i]=0;
  }


  for(i = 2; i*i < 1100000; i++){
    if(data[i]==0){
      for(j = 2*i; j < 1100000; j+=i){
	data[j]=1;
      }
    }
  }
  data[0]=1;
  data[1]=1;
 
  while(1){
    result.clear();
    cin >> n >> p;
    if(n==-1 && p==-1)break;
    j = 0;
    for(i = n+1; i < 1100000; i++){
      if(data[i]==0){
	primenum[j]=i;
	j++;
	if(j==1000)break;
      }
    }

    //for(i = 0; i < 30; i++){
    // cout <<"primenum[" << i << "]" << primenum[i] << endl;
    // }
      for(i = 0;i < 100; i++){
	for(k = i; k < 100; k++){
	result.push_back(primenum[i]+primenum[k]);
	//	cout << "primenum[i]" <<primenum[i] <<"primenum[k]" << primenum[k] << endl;
	}
      }

     
      
      sort(result.begin(),result.end());
      // for(i = 0; i < 100; i++){
      //	cout << "result[" <<i<< "]"<<result[i] << endl;
      // }
      cout << result[p-1] << endl;
      
    }
   return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
template <class T> inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T> inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return 1;
    }
    return 0;
}
typedef long long int ll;

#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define endl "\n"
const double EPS = 1e-7;
const int INF = 1 << 30;
const ll LLINF = 1LL << 60;
const double PI = acos(-1);
const int MOD = 1000000007;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

//-------------------------------------

void makePrimeTable(vector<bool> &isPrime, int n) {
    isPrime.resize(n + 1, true);
    isPrime[0] = false;
    isPrime[1] = false;
    for(int i = 2; i * i <= n; i++) {
        if(isPrime[i]) {
            for(int j = 2; i * j <= n; j++) {
                isPrime[i * j] = false;
            }
        }
    }
}

vector<bool> isPrime;

void solve(ll n, ll p) {
    vector<ll> kouho;
    ll now = n + 1;
    while(kouho.size() < p) {
        if(isPrime[now]) {
            kouho.emplace_back(now);
        }
        now++;
    }
    sort(ALL(kouho));
    vector<ll> res;
    for(ll i = 0; i < kouho.size(); i++) {
        for(ll j = i; j < kouho.size(); j++) {
            res.emplace_back(kouho[i] + kouho[j]);
        }
    }
    sort(ALL(res));
    cout << res[p - 1] << endl;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    makePrimeTable(isPrime, 1000100);
    while(1) {
        ll n, p;
        cin >> n >> p;
        if(n == -1 && p == -1) {
            break;
        }
        solve(n, p);
    }
}

C++: #include <vector>
#include <iostream>
#include <algorithm>
 
using namespace std;
 
bool is_prime(int n, int k = 3)
{
    if(n < k * k) { return true; }
     
    if(n % k == 0) { return false; }
     
    return is_prime(n, k + 2);
}
 
int main()
{
    vector<int> prime = {2};
     
    for(int i = 3; i < 101300; i += 2)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
     
    int n, m;
     
    while(true)
    {
        scanf("%d", &n);
        scanf("%d", &m);
         
        if(n == -1 && m == -1) { break; }
         
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
         
        vector<int> c; int r = min(50, m) - 1;
        
        for(int i = ptr + r; i >= ptr; i--)
        {
            for(int j = ptr + r; j >= i; j--)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
        
        sort(c.begin(), c.end());
         
        printf("%d\n", c[m - 1]);
    }
     
    return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

#define MAX (300001)

bool is_prime[MAX+1];
vector<long long> prime;
int size;

void Sieve() {
  fill(is_prime, is_prime+MAX, true);
  
  is_prime[0] = is_prime[1] = false;
  
  for(long long i=2; i<=MAX; i++) {
    if(is_prime[i]) {
      prime.push_back(i);
      for(long long j=i*i; j<=MAX; j+=i) {
	is_prime[j] = false;
      }
    }
  }
}

int main() {
  int n, p;
  
  Sieve();
  
  while(cin >> n >> p, !(n == -1 && p == -1)) {
    int st = upper_bound(prime.begin(), prime.end(), n) - prime.begin();
    vector<long long> vec;
    for(int i=st; i<=st+p; i++) {
      for(int j=i; j<=st+p; j++) {
	vec.push_back(prime[i]+prime[j]);
      }
    }
    sort(vec.begin(), vec.end());
    cout << vec[p-1] << endl;
  }
  
  return 0;
}