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>
#include <cmath>
#include <algorithm>

using std::cin;
using std::cout;
using std::endl;

bool is_prime(int n) {
	if (n < 2) {
			return false;
	}
	if (n==2||n==3) {
		return true;
	}
	for (int i = 3; i < n; i = i+2) {
		if (n%i==0) {
			return false;
		}
	}
	return true;
}

int check_ind(std::vector<int> v, int n) {
	int ind = 0;
	for (std::vector<int>::iterator itr = v.begin(); itr != v.end(); ++itr) {
		if (*itr > n) {
			return ind;
		}
		ind++;
	}
	return 0;
}

int main(void) {
	int n = 101000;
	std::vector<bool> prime(n);
	std::vector<int> p;
	for (int i = 0; i < n+2; i++) {
		prime[i] = true;
	}
	prime[0] = false;
	prime[1] = false;
	for (int i = 2; i <= sqrt(n); i++) {
		if (is_prime(i)) {
			for (int j = 2; i*j < n+2; j++) {
				prime[i*j] = false;
			}
		}
	}
	for (int i = 2; i < n+2; i++) {
		if (prime[i]) {
			p.push_back(i);
		}
	}

	int N,P;
	cin >> N;
	cin >> P;

	while (N != -1 || P != -1) {
		int ind = check_ind(p, N);
		std::vector<int> sum;

		for (int i = ind; i < ind+(2*sqrt(P)); i++) {
			for (int j = i; j < i+(2*sqrt(P)); j++) {
				sum.push_back(p[i]+p[j]);
			}
		}

		std::sort(sum.begin(), sum.end());

		cout << sum[P-1] << endl;

		cin >> N;
		cin >> P;
	}

	return 0;
}

C++: import java.util.*;
public class Main {
	
	void doIt() {
		Scanner stdIn = new Scanner(System.in);
		while(true) {
			int N = stdIn.nextInt();
			int P = stdIn.nextInt();
			if(N == -1 && P == -1) break;
			ArrayList<Integer> list = new ArrayList<Integer>(100);
			
			int num = N;
			while(list.size() < 100) {
				boolean flag = true; //素数であると仮定
				if(N == 1) flag = false; //Nが１であればもう見る必要は無い
				for(int c = 2; c <= Math.sqrt(N); c++) {//素数であるか見てみる
					if(N % c == 0) { 
						flag = false;
						break;
					}
				}
				if(flag) list.add(N);
				N++;
			}
		
			for(int r = 0; r < list.size(); r++) {
				if(list.get(r) > num) { 
					num = r; //添字にする 
					break;
				}
			}
			
			ArrayList<Integer> output = new ArrayList<Integer>();
			for(int r = num; r < list.size(); r++) {
				for(int c = r; c < list.size(); c++) {
					output.add(list.get(r) + list.get(c));
				}
			}
			Collections.sort(output);
			System.out.println(output.get(P - 1));
		}
	}
	
	public static void main(String[] args) {
		new Main().doIt();
	}
}

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

using namespace std;

const int MAX = 1000000;
bool prime[MAX];
vector<int> V;
int N,P;

void make(){
  memset(prime,true,sizeof(prime));

  prime[0] = prime[1] = false;

  for(int i = 2; i*i < MAX; i++)
    if(prime[i])
      for(int j = 2; i*j < MAX; j++)
	prime[i*j] = false;

  for(int i = 0; i < MAX; i++)
    if(prime[i]) V.push_back(i);
 
}

void solve(){

  vector<int> M;
  vector<int>::iterator ite = upper_bound(V.begin(),V.end(),N);

  for(vector<int>::iterator i = ite; i < ite+200; i++)
    for(vector<int>::iterator j = i; j < ite+200; j++)
      M.push_back(*i+*j);

  sort(M.begin(),M.end());

  cout << M[P-1] << endl;
}

int main(){
  make();
  while(cin >> N >> P){
    if(N == -1 && P == -1) break;
    solve();
  }
  return 0;
}

C++: #include "bits/stdc++.h"

#define REP(i,n) for(ll i=0;i<n;++i)
#define RREP(i,n) for(ll i=n-1;i>=0;--i)
#define FOR(i,m,n) for(ll i=m;i<n;++i)
#define RFOR(i,m,n) for(ll i=n-1;i>=m;--i)
#define ALL(v) (v).begin(),(v).end()
#define PB(a) push_back(a)
#define UNIQUE(v) v.erase(unique(ALL(v),v.end()));
#define DUMP(v) REP(i, (v).size()) { cout << v[i]; if (i != v.size() - 1)cout << " "; else cout << endl; }
#define INF 1000000001ll
#define MOD 1000000007ll
#define EPS 1e-9

const int dx[8] = { 1,1,0,-1,-1,-1,0,1 };
const int dy[8] = { 0,1,1,1,0,-1,-1,-1 };


using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
///(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)///
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	vl prime = { 2 };
	FOR(i, 3,114514) {
		int flag = 1;
		REP(j, prime.size()) {
			if (i%prime[j] == 0)flag = 0;
		}
		if (flag)prime.push_back(i);
	}

	int n, p;
	while (1) {
		cin >> n >> p;
		if (n == -1)break;
		int c = lower_bound(ALL(prime), n) - prime.begin();
		vl v(p*p);
		REP(i, p) {
			REP(j, p) {
				v[i*p + j] = prime[i+c] + prime[j+c];
			}
		}
		sort(ALL(v));
		cout << v[p - 1] << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<string>
#include<cmath>
#include<algorithm>
#include<set>
using namespace std;
vector<int>a;
bool b[1000000];
int main() {
	fill(b,b+1000000, true);
	b[0] = false; b[1] = false;
	for (int i = 2; i < 1000000; i++) {
		if (b[i]) {
			a.push_back(i);
			int j = 2;
			while (i*j < 1000000) {
				b[i*j] = false;
				j++;
			}
		}
	}
	int n=0, p=55;
	while (cin >> n >> p&&n != -1) {
		int c = sqrt(p) + 2;
		int i = 0;
		while (a[i] < n) i++;
		multiset <long long>d;
		for (int j = i; j <= i + c; j++) {
			for (int z = i; z <= i + c; j++) {
				d.insert(i+j);
			}
		}
		multiset<long long>::iterator it = d.begin();
		for (int i = 0; i < p; i++) {
			it++;
		}
		cout << (*it) << endl;
	}
}