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 <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
#include <cstring>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
#define CLR(mat) memset(mat, 0, sizeof(mat))
typedef long long ll;
const ll MAX = 500000;
bool isPrime[MAX];
vector<ll> prime;
void makePrime(){
  for (ll i = 0; i < MAX; i++){
    isPrime[i] = true;
  }
  for (ll i = 2; i * i < MAX + 1; i++){
    if(isPrime[i]){
      for (ll j = 2 * i; j < MAX; j += i) {
        isPrime[j] = false;
      }
    }
  }
  FOR(i,2,MAX) if(isPrime[i]) prime.push_back(i);
  return;
}
int main()
{
  makePrime();
  int N, R;
  while(cin >> N >> R, N != -1) {
    int j = upper_bound(prime.begin(), prime.end(), N) - prime.begin();
    vector<int> v;
    FOR(i,j,j+200) {
      FOR(k,i,j+200) {
        v.push_back(prime[i]+prime[k]);
      }
    }
    sort(v.begin(), v.end());
    cout << v[R-1] << endl;
  }
  return 0;
}

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; m--;
        
        for(int i = ptr + m; i >= ptr; i--)
        {
            for(int j = ptr + m; 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 <bits/stdc++.h>

using namespace std;

int p[200001];

int main()
{
    p[0] = 1;
    p[1] = 1;
    for (int i = 4; i <= 200000; i += 2) p[i] = 1;
    
    for (int i = 3; i * i <= 200000; i += 2){
        if (!p[i]){
            for (int j = i * 3; j <= 200000; j += 2 * i) p[j] = 1;
        }
    }
    
    int N, P;
    
    while (scanf("%d %d", &N, &P) && ~N){
        vector<int> v, v2;
        
        for (int i = N; ; i++){
            if (!p[i]) v.push_back(i);
            if (v.size() == 20) break;
        }
        
        for (int i = 0; i < 20; i++){
            for (int j = i; j < 20; j++){
                v2.push_back(v[i] + v[j]);
            }
        }
        sort(v2.begin(), v2.end());
        
        printf("%d\n", v2[P - 1]);
    }
    
    return (0);
}

C++: #include <bits/stdc++.h>
#define _overload3(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for (ll i = (ll)(a); i < (ll)(b); ++i)
#define rep(...) _overload3(__VA_ARGS__, repi, _rep, )(__VA_ARGS__)
#define ll long long
#define lld long double
#define ALL(x) x.begin(), x.end()
#ifdef DEBUG
#define line() cerr << "[" << __LINE__ << "] ";
#define dump(i) cerr << #i ": " << i << " ";
#define dumpl(i) cerr << #i ": " << i << endl;
#else
#define line(i)
#define dump(i)
#define dumpl(i)
#endif
using namespace std;

void prime(vector<int> &v)
{
    v.push_back(2);
    rep(i, 3, 201010)
    {
        bool flg = true;
        for (auto p : v)
        {
            if (i % p == 0)
            {
                flg = false;
                break;
            }
        }
        if (flg == true)
        {
            v.push_back(i);
        }
    }
}

int main()
{
    vector<int> v;
    prime(v);
    while (true)
    {
        map<int, bool> mp;
        int n, p;
        cin >> n >> p;
        if (n == -1 && p == -1)
        {
            break;
        }
        int q = p / 2; //sqrt(p) + 1;
        int start = upper_bound(v.begin(), v.end(), n) - v.begin();
        // cerr << start << endl;
        vector<int> ans;
        rep(i, start, start + 2 * p)
        {
            rep(j, i, start + 2 * p)
            {
                //   cerr << v[i] + v[j] << endl;
                // if (mp[v[i] + v[j]] == false)

                //                {
                ans.push_back(v[i] + v[j]);
                //                  mp[v[i] + v[j]] = true;
                //            }
            }
        }
        sort(ans.begin(), ans.end());

        //cerr << ans.size() << endl;
        //rep(i, ans.size())
        //{
        //    cerr << ans[i] << " ";
        //}
        // cerr << endl;
        cout << ans[p - 1] << endl;
    }

    return 0;
}