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>

#define REP(i, n) for (int i = 0; i < n; i++)
#define ALL(obj) obj.begin(), obj.end()
#define fcout cout << setprecision(10)

const int iINF = 1e9;
const long long llINF = 1e18;
const int MOD = 1e9 + 7;

using namespace std;

template <typename T>
void debug(vector<T> &vec) {
    for (auto x : vec) {
        cout << x << " ";
    }
    cout << endl;
    return;
}

template<typename A, size_t N, typename T>
void FILL(A (&array)[N], const T &val){
    std::fill( (T*)array, (T*)(array+N), val );
}

template <typename T>
int getFormer(const vector<T> &vec, T x) {
    return upper_bound(vec.begin(), vec.end(), x) - vec.begin() - 1;
}

template <typename T>
int getLatter(const vector<T> &vec, T x) {
    return lower_bound(vec.begin(), vec.end(), x) - vec.begin();
}

vector<long long> era(int N) {
    vector<bool> isPrime(N, true);
    vector<long long> res;
    isPrime[0] = isPrime[1] = false;
    for (int i = 2; i < sqrt(N) + 1; i++) {
        if (isPrime[i] == true) {
            for (int j = i + i; j < N + 1; j += i){
                isPrime[j] = false;
            }
        }
    }

    for (int i = 2; i < N + 1; i++) {
        if (isPrime[i] == true) res.push_back(i);
    }

    return res;
}

vector<long long> primes;

int solve(int N, int P) {
    auto s = lower_bound(ALL(primes), N) - primes.begin();
    vector<long long> sums;
    for (int i = s; i < s + P + 1; i++) {
        for (int j = i; j < s + P + 1; j++) {
            sums.push_back(primes[i] + primes[j]);
        }
    }

    sort(ALL(sums));
    cout << sums[P - 1] << endl;
}

int main() {
    int N, P;
    primes = era(3 * 1e5);
    while (cin >> N >> P && N != -1) {
        solve(N, P);
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#define MAX_N 10000000

using namespace std;

int prime[MAX_N];
bool is_prime[MAX_N + 1];
int size;

int sieve(int n){
  int p = 0;
  for(int i=0;i<=n;i++){
    is_prime[i] = true;
  }
  is_prime[0] = is_prime[1] = false;
  for(int i=2;i<=n;i++){
    if(is_prime[i]){
      prime[p++] = i;
      for(int j=2*i;j<=n;j+=i) is_prime[j] = false;
    }
  }
  return p;
}

main(){
  size = sieve(MAX_N);
  int n, p;
  while(cin >> n >> p){
    if(n == -1 && p == -1) break;
    vector<int> data;
    data.clear();
    int r, l;
    for(int i=0;i<size;i++){
      if(i == size){
	r = l = i;
	break;
      }
      if(prime[i]>n){
	r = l = i;
	break;
      }
    }
    for(int i=0;i<=p;i++){
      for(int j=i;j<=p;j++){
	data.push_back(prime[r+i]+prime[r+j]);
      }
    }
    sort(data.begin(), data.end());
    cout << data[p-1] << endl;
  }
  return 0;
}

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;
        
        for(int i = ptr + m - 1; i >= ptr; i--)
        {
            for(int j = ptr + m - 1; 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<string>
#include<cmath>
#include<queue>
#include<vector>
#include<functional>
using namespace std;
bool a[200000];
int main() {
	fill(a, a + 200000, true);
	a[0] = false; a[1] = false;
	for (int i = 0; i < 200000; i++) {
		if (a[i]) {
			int j = 2;
			while (i*j < 200000) {
				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 < 200000 && 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;
	}
}