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<string>
#include<cmath>
#include<queue>
#include<vector>
#include<functional>
#include<algorithm>
using namespace std;
bool a[300000];
int main() {
	fill(a, a + 300000, true);
	a[0] = false; a[1] = false;
	for (int i = 0; i < 300000; i++) {
		if (a[i]) {
			int j = 2;
			while (i*j < 300000) {
				a[i*j] = false;
				j++;
			}
		}
	}
	int n, p;
	while (cin >> n >> p&&n != -1 && p != -1) {
		int sum = 0;
		int b[1000];
		for (int i = n; i < 300000 && sum <= p; i++) {
			if (a[i]) {
				b[sum] = i;
				sum++;
			}
		}
		int c[10000];
		int sum2 = 0;
		for (int i = 0; i < sum; i++) {
			for (int j = i; j < sum; j++) {
				c[sum2] = b[i] + b[j];
				sum2++;
			}
		}
		sort(c, c + sum2);
		cout << c[p - 1] << endl;
	}
}

C++: #include <bits/stdc++.h>
#define REP(i,n,N) for(int i=n;i<N;i++)
#define p(S) cout<<S<<endl
using namespace std;

bool mprime[200000]={false};

void matuPrime(){
	mprime[0] = mprime[1] = true;
	for(int i=2;i*i<=200000;i++){
		for(int j=i*2;j<=200000;j+=i){
			mprime[j]=true;
		}
	}
}

int main(){
	int N,P;
	matuPrime();
	while(cin>>N>>P&&N!=-1){
		vector<int> vt,sum;
		for(unsigned int i=N+1;sum.size()<2*P;i++){
			if(!mprime[i]){
				vt.push_back(i);
				for(unsigned int j=0;j<vt.size();j++){
					sum.push_back(i+vt[j]);
				}
			}
		}
		sort(sum.begin(),sum.end());
		p(sum[P-1]);
	}
	return 0;
}

C++: #include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(int)(a); (i)<(int)(b); ++(i))
#define rFor(i, a, b) for(int (i)=(int)(a)-1; (i)>=(int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<int, lint> pil;
typedef pair<lint, lint> pll;
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(a>b){a=b; return true;} return false;}

constexpr lint mod = 1e9+7;
constexpr lint INF = mod*mod;
constexpr int MAX = 100010;

vector<int> min_factor, prime;

void sieve(int n){
    min_factor.resize(n+1, 0);
    For(i, 2, n+1){
        if(min_factor[i] == 0){
            min_factor[i] = i;
            prime.push_back(i);
        }
        for(int x: prime){
            if(x*i > n || x > i) break;
            min_factor[x*i] = x;
        }
    }
}

int main(){
    sieve(1000000);
    int n, p;
    while(scanf("%d%d", &n, &p) && n>=0){
        auto cmp = [&](pii a, pii b){
            return prime[a.fi]+prime[a.se] > prime[b.fi]+prime[b.se];
        };
        priority_queue<pii, vector<pii>, decltype(cmp)> que(cmp);
        int idx = upper_bound(prime.begin(), prime.end(), n) - prime.begin();
        que.emplace(idx, idx);
        set<pii> S;
        rep(_, p-1){
            pii t = que.top();
            que.pop();
            pii u = {t.fi+1, t.se}, v = {t.fi, t.se+1};
            if(u.fi > u.se) swap(u.fi, u.se);
            if(v.fi > v.se) swap(v.fi, v.se);
            if(S.find(u) == S.end()){
                que.push(u);
                S.insert(u);
            }
            if(S.find(v) == S.end()){
                que.push(v);
                S.insert(v);
            }
        }
        pii t = que.top();
        printf("%d\n", prime[t.fi]+prime[t.se]);
    }
}

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

using namespace std;

const int K=150000;
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;
}