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 <math.h>
#include <algorithm>
using namespace std;
int main(){
	int n,p;
	while(cin>>n>>p){
		if(n==-1&&p==-1) break;
		int a[p][2],so[p];
		for(int i=0;i<p;i++){
			a[i][0]=0;
			a[i][1]=0;
		}
		int ct=0,nn=n+1;
		while(ct<p){
			if(nn%2==0&&nn!=2){
				goto end;
			}
			else if(nn%3==0&&nn!=3){
				goto end;
			}
			for(int i=1;i<(sqrt(nn)/6)+3;i++){
				if(nn%(6*i+1)==0&&6*i+1!=nn) goto end;
				if(nn%(6*i-1)==0&&6*i-1!=nn) goto end;
			}
			if(nn==1) goto end;
			so[ct]=nn;
			ct++;
			end:;
			nn++;
		}
		int wa=2*n+2,c=0;
		while (c<p){
			for(int i=0;i<p;i++){
				for(int j=0;j<=i;j++){
					if(so[i]+so[j]==wa){
						a[c][0]=min(so[i],so[j]);
						a[c][1]=max(so[i],so[j]);
						c++;
						if(c==p){
							goto endend;
						}
					}
				}
			}
			wa++;
		}
		endend:;
		cout<<a[p-1][0]+a[p-1][1]<<endl;
	}
    return 0;
}

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

vector<int> sieve(int n) {
	vector<int> res(1, 2);
	vector<bool> prime(n, true);
	for(int i = 3; i < n; i += 2) {
		if(prime[i]) {
			res.push_back(i);
			for(int j = i * 3; j < n; j += i * 2)
				prime[j] = false;
		}
	}

	return res;
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	const int MAX = 120000;
	const vector<int> primes = sieve(MAX);
	for(int n, p; cin >> n >> p, n != -1;) {
		const int start = upper_bound(primes.begin(), primes.end(), n) - primes.begin();
		vector<int> nums;
		nums.reserve(6000);
		for(int i = start; i < start + 100; ++i)
			for(int j = i; j < start + 100; ++j)
				nums.push_back(primes[i] + primes[j]);

		sort(nums.begin(), nums.end());
		cout << nums[p - 1] << endl;
	}

	return EXIT_SUCCESS;
}

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

using namespace std;

int main() {
	vector<bool> isprime(200000, true);
	isprime[0] = isprime[1] = false;
	vector<int> prime;
	for (long long i = 2; i < 200000; ++i) {
		if (isprime[i]) {
			prime.push_back(i);
			for (long long j = i * i; j < 200000; j += i) isprime[j] = false;
		}
	}
	int n, p;
	while (cin >> n >> p, n >= 0) {
		auto it = upper_bound(prime.begin(), prime.end(), n);
		vector<int> tmp, ans;
		for (int i = 0; i < 100; ++i) tmp.push_back(*it++);
		for (int i = 0; i < 100; ++i)
			for (int j = i; j < 100; ++j)
				ans.push_back(tmp[i] + tmp[j]);
		sort(ans.begin(), ans.end());
		cout << ans[p - 1] << endl;
	}

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

using ll=long long;
#define int ll

#define FOR(i,a,b) for(int i=int(a);i<int(b);i++)
#define REP(i,b) FOR(i,0,b)

int read(){
  int i;
  scanf("%lld",&i);
  return i;
}

bool is_prime(int n){
  if(n==0||n==1) return false;
  if(n==2) return true;
  for(int i=2;i*i<=n;i++){
    if(n%i==0) return false;
  }
  return true;
}

signed main(){
  while(true){
    int N=read(),P=read();
    if(N==-1&&P==-1) break;
    vector<int> prime;
    vector<int> matsuzaki;
    ++N;
    while(1){ // O(P)
      if(is_prime(N)){
        prime.push_back(N);
        REP(j,prime.size()){ // O(P)
          matsuzaki.push_back(prime[j]+N);
        }
        if(prime.size()>=P){
          break;
        }
      }
      N++;
    }
    sort(matsuzaki.begin(),matsuzaki.end());
    cout << matsuzaki[P - 1] << endl;
  }    
}