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 <algorithm>
#include <queue>
#include <cmath>
#include <cassert>

using namespace std;

int main()
{
    const int N = 100000;

    bool is_not_prime[2*N] = { true, true, false };
    
    int const lim = ceil( sqrt( 2*N ) );
    for( int i=2; i<lim; ++i ) {
        if ( !is_not_prime[i] ) {
            for( int j=i+i; j<2*N; j+=i ) {
                is_not_prime[j] = true;
            }
        }
    }

    auto is_prime = [&]( size_t const& i ){ return !is_not_prime[i]; };

    int primes[N];
    size_t const max_prime_index = [&]() mutable
    {
        size_t index = 0;
        for( int i=0; i<2*N; ++i ) {
            if ( is_prime( i ) ) {
                primes[index++] = i;
            }
        }

        return index;
    }();

    int n, p;
    while( cin >> n >> p ) {
        if ( n == -1 && p == -1 )
            break;

        int base = -1;
        for( int i=n+1; i<2*N; ++i ) {
            if ( is_prime( i ) ) {
                base = i;
                break;
            }
        }
        assert( base != -1 );
        auto it = find( primes, primes + max_prime_index, base );

        vector<int> px;
        for( int i=0; i<p; ++i ) {
            for( int j=i; j<p; ++j ) {
                px.push_back( *(it + i) + *(it + j) );
            }
        }
        sort( px.begin(), px.end() );

        cout << px[p-1] << endl;
    }
}

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

using namespace std;

int main()
{
  bool isPrime[1000001];
  for(int i = 0; i <= 1000000; i++) isPrime[i] = true;
  isPrime[0] = isPrime[1] = false;
  for(int i = 2; i <= 1000000; i++){
    if(isPrime[i]){
      for(int j = i+i; j <= 1000000; j += i) isPrime[j] = false;
    }
  }

  int N, P;
  while(cin >> N >> P, N != -1 || P != -1){
    int prime[100];
    for(int i = N + 1, j = 0; j < 100; i++){
      if(isPrime[i]) prime[j] = i, j++;
    }
    int matsu[10000];
    int idx = 0;
    for(int i = 0; i < 100; i++){
      for(int j = i; j < 100; j++){
	matsu[idx] = prime[i]+prime[j], idx++;
      }
    }
    sort(matsu, matsu + idx);
    cout << matsu[P-1] << endl;
  }
  return 0;
}

C++: #include <iostream>
using namespace std;
bool prime[300005];

void init(void){
  for(int i = 0 ; i < 300005 ; i++){prime[i] = true;}
  prime[0] = false, prime[1] = false;
  for(int i = 2 ; i < 300005 ; i++){
    if(prime[i] == true){
      for(int k = 2 ; i * k < 300005 ; k++){
	prime[i * k] = false;
      }
    }
  }
}

int main(void){
    init();
    for(;;){
        int N, P;
        cin >> N >> P;
	if(N == -1 && P == -1){return 0;}
        int p[100];
        int ptr=0;
        for(int i = N + 1 ; ptr<100 ; i++){
            if(prime[i]){p[ptr] = i; ptr++;}
        }
        int sum[50*101]; ptr=0;
        for(int i = 0 ; i < 100 ; i++){
            for(int j = i ; j < 100 ; j++){
                sum[ptr] = p[i] + p[j]; ptr++;
            }
        }
        for(int i = 0 ; i < 5050 ; i++){
            for(int j = i+1 ; j < 5050 ; j++){
                if(sum[i] > sum[j]){
                    int temp = sum[i];
                    sum[i] = sum[j];
                    sum[j] = temp;
                }
            }
        }
        cout << sum[P-1] << endl;
    }
}

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(22, 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;
}