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 <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; int r = min(15, m) - 1;
        
        for(int i = ptr + r; i >= ptr; i--)
        {
            for(int j = ptr + r; 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<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
  int n,p;
  int prime[101000];

  for(int i=0;i<101000;i+=2)prime[i] = 0;
  for(int i=1;i<101000;i+=2)prime[i] = 1;
  prime[1] = 0;
  prime[2] = 1;

  int c = 3;
  while(c*c<101000){
    for(int i=3*c;i<101000;i+=c)prime[i] = 0;
    while(!prime[++c]);
  }

  while(1){
    cin >> n >> p;
    if(n<0 && p<0)break;

    vector<int> e;
    for(int i=0;i<p;i++){
      while(!prime[++n]);
      e.push_back(n);
    }

    vector<int> c;
    for(int i=0;i<(int)e.size();i++){
      for(int j=i;j<(int)e.size();j++){
	c.push_back(e[i] + e[j]);
      }
    }

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

C++: #include<iostream>
#include<string>
#include<algorithm>
using namespace std;
long long m[100],c[10000],prime[200];
int main(){
	long long n,p;
	int count=0,i=2;
	while(true){
		bool t=true;
		for(int j=2;j*j<=i;j++){
			if(i%j==0)
				t=false;
		}
		if(t==true){
			prime[count]=i;
			count++;
		}
		if(count==200)
			break;
		i++;
	}
	while(true){
		cin>>n>>p;
		if(n==-1&&p==-1)
			break;
		for(int i=0;i<p*p;i++){
			c[i]=1000000;
		}
		if(n==0)
			n++;
		int i=n+1,count=0;
		while(true){
			bool t=true;
			for(int j=0;j<200;j++){
				if(i!=prime[j]&&i%prime[j]==0)
					t=false;
			}
			if(t==true){
				m[count]=i;
				count++;
			}
			if(count==p)
				break;
			if(i%2==1)
				i+=2;
			else
			i++;
		}
		for(int i=0;i<p;i++){
			for(int j=0;j<=i;j++){
				c[i*p+j]=m[i]+m[j];
			}
		}
		sort(c,c+p*p);
		cout<<c[p-1]<<endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define all(c) (c).begin(), (c).end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

bool isPrime[2 * 100105];
vector<int> primes;

int N, P;
void solve() {
    vector<int> vec;
    // cout << primes.size() << endl;
    int idx = upper_bound(all(primes), N) - primes.begin();
    // cout << "idx = " << idx << endl;
    for (int i = idx; i < idx + P; i++) {
        for (int j = idx; j < idx + P; j++) {
            if (primes[i] > primes[j]) continue;
            // if (primes[i] == 3) cout << primes[i] << " + " << primes[j] << endl;
            vec.push_back(primes[i] + primes[j]);
        }
    }
    sort(all(vec));
    // rep(i, P) cout << i << ": " << vec[i] << endl;
    cout << vec[P - 1] << endl;
}
int main() {
    rep(i, 2 * 100105) isPrime[i] = true;
    isPrime[0] = isPrime[1] = false;
    rep(i, 2 * 100105) if (i > 1) {
        if (isPrime[i]) {
            for (int j = i * 2; j < 2 * 100105; j += i) isPrime[j] = false;
        }
    }
    rep(i, 2 * 100105) if (isPrime[i]) primes.push_back(i);
    while (cin >> N >> P, P != -1) {
        solve();
    }

    return 0;
}