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 <bits/stdc++.h>

using namespace std;

#define REP(i, n) for (int i=0; i<(n); ++i)
#define RREP(i, n) for (int i=(int)(n)-1; i>=0; --i)
#define FOR(i, a, n) for (int i=(a); i<(n); ++i)
#define RFOR(i, a, n) for (int i=(int)(n)-1; i>=(a); --i)

#define SZ(x) ((int)(x).size())
#define all(x) begin(x),end(x)

#define dump(x) cerr<<#x<<" = "<<(x)<<endl
#define debug(x) cerr<<#x<<" = "<<(x)<<" (L"<<__LINE__<<")"<<endl;

template<class T>
ostream &operator<<(ostream &os, const vector <T> &v) {
    os << "[";
    REP(i, SZ(v)) {
        if (i) os << ", ";
        os << v[i];
    }
    return os << "]";
}

template<class T, class U>
ostream &operator<<(ostream &os, const pair <T, U> &p) {
    return os << "(" << p.first << " " << p.second << ")";
}

template<class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;

const ll MOD = 1e9 + 7;
const int INF = INT_MAX / 2;
const ll LINF = LLONG_MAX / 2;
const ld EPS = 1e-9;


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    const int MAX = 1e6;
    vi prime(MAX, 1);
    prime[0] = prime[1] = 0;
    for (int i = 2; i * i < MAX; ++i) {
        if (!prime[i]) continue;
        for (int j = 2*i; j < MAX; j += i) {
            prime[j] = 0;
        }
    }

    for (;;) {
        int N, P; cin >> N >> P;
        if (N == -1) break;
        vi primes;
        for (int i = N+1; i < MAX; ++i) {
            if (prime[i]) primes.push_back(i);
        }
        vi sum;
        REP(i, min(P, SZ(primes))) {
            FOR(j, i, min(P, SZ(primes))) {
                sum.push_back(primes[i] + primes[j]);
            }
        }
        sort(all(sum));
        cout << sum[P-1] << endl;
    }

    return 0;
}

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

using namespace std;

const int K=100100100;
bool A[K];
vector<int> prime;
void F(){
   for(int i=0; i<K; i++) A[i]=true;

   A[0]=A[1]=false;
   for(int i=0; i*i<=K; i++){
      if(A[i])for(int j=2; (i*j)<K; j++){
         A[i*j]=false;
      }
   }
   for(int i=0; i<K; i++){
      if(A[i]) prime.push_back(i);
   }
}

signed main(){

   F();
   while(1){
      int N, P;
      cin>> N>> P;
      if(N==-1&&P==-1) break;

      N++;
      vector<int> v;
      while(A[N]==false) N++;
      for(int i=0; i<prime.size(); i++){
         if(prime[i]<N) continue;
         for(int j=0; j<P; j++){
            v.push_back(prime[i]+prime[i+j]);
         }
      }
      sort(v.begin(), v.end());

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

   return 0;
}

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

const int MAX_N = 210000;

// p[i] := i 番目の素数
vector<int> p;
// is_p[i] := i が素数のとき true
bool is_p[MAX_N+1] = {false,false};

// エラトステネスのふるい
void sieve(){
	for(int i=2 ; i <= MAX_N ; i++ )
		is_p[i] = true;
	for(int i=2 ; i*i <= MAX_N ; i++ ){
		if( is_p[i] ){
			p.push_back( i );
			for(int j = i+i ; j <= MAX_N ; j += i ){
				is_p[j] = false;
			}
		}
	}
}

// N より大きい任意の2つ素数を足したものの中で P 番目に小さい数値を返す
int M(int N, int P){
	int id;
	for(int i=0 ; i < p.size() ; i++ ){
		if( p[i] > N ){
			id = i;
			break;
		}
	}
	priority_queue<int> q;
	//vector<int> v;
	for(int i = id ; i < id+P ; i++ ){
		for(int j = i ; j < id+P ; j++ ){
			q.push( -p[i] - p[j] );
			//v.push_back( p[i] + p[j] );
		}
	}
	//sort( v.begin() , v.end() );
	//if( P-1 >= v.size() ) return v[v.size()-1];
	//return v[P-1];
	int result;
	for(int i=0 ; i < P ; i++ ){
		result = q.top(); q.pop();
	}
	return -result;
}

int main(){
	int n,p;
	sieve();
	while( cin >> n >> p , n != -1 ){
		cout << M(n,p) << endl;
	}
}