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 <queue>
#include <cctype>
#include <stdio.h>
#include <map>
#include <string.h>
#include <algorithm>
#include <vector>

using namespace std;

int max(int a, int b);
int min(int a, int b);
int is_prime(int n);

int main(int argc, char const* argv[])
{
    int n,p;
    while (cin >> n >> p) 
    {
        if ( n==-1 && p==-1 ) { break; }
        vector<int> arr;

        //テァツエツ?ヲツ閉ーテ・ツ按療」ツつ津ヲツ?シテァツエツ?
        int count=0;
        int i=n+1;
        while ( count <  p ) 
        {
            if ( is_prime(i) ) 
            {
                //cout << "i = " << i << endl;
                arr.push_back(i);    
                count++;
            }
            i++;
        }

        //
        //for (int i = 0; i < p; i++) 
        //{
        //    cout << arr[i] << endl;
        //}

        //ティツカツウテ」ツ?療」ツ?淌ァツエツ?ヲツ閉ーテ」ツつ津ヲツ?シテァツエツ?
        vector<int> sum;
        for (int i = 0; i < p; i++) 
        {
            for (int j = i; j < p; j++) 
            {
                sum.push_back( arr[i] + arr[j] );
            }
        }
        sort(sum.begin(), sum.end());
        cout << sum[p-1] << endl;    
    }
    return 0;
}

int is_prime(int n)
{
    if (n ==1 || n== 0) 
    {
        return 0;
    }
    for (int i = 2; i*i <= n; i++) 
    {
        if (n % i == 0) 
        {
            return 0;
        }
    }
    return 1;

}


int max(int a, int b)
{
    if (a > b) 
    {
        return a;
    }
    else{
        return b;
    }
}
int min(int a, int b)
{
    if (a > b) 
    {
        return b;
    }
    else{
        return a;
    }
}

C++: #include <algorithm>
#include <bitset>
#include <functional>
#include <iostream>
#include <queue>
#include <vector>

using namespace std;

int main()
{
    const auto primes = [] {
        vector<int> r;
        bitset<1'000'000> b;
        auto t = b;
        t.set();
        t[0] = false;
        t[1] = false;
        int i = 0;
        while (true) {
            bool done = false;
            while (!t[i]) {
                ++i;
                if (i == t.size()) {
                    done = true;
                    break;
                }
            }
            if (done) {
                break;
            }

            b[i] = true;
            r.push_back(i);
            for (int j = i; j < t.size(); j += i) {
                t[j] = false;
            }
        }
        return r;
    }();

    while (true) {
        int n, p;
        cin >> n >> p;
        if (n == -1 && p == -1) {
            return 0;
        }

        const auto s = upper_bound(begin(primes), end(primes), n);
        vector<int> q;
        for (int i = 0; i < p; ++i) {
            for (int j = i; j < p; ++j) {
                q.push_back(*(s + i) + *(s + j));
            }
        }
        sort(begin(q), end(q));
        cout << q[p - 1] << endl;
    }
}

C++: // {{{ include and macros
#define debug(x) cout<<#x<<": "<<x<<endl
#define rep(i, a, b) for(int i=a; i < b;i++)
#include <algorithm>
#include <iostream>
#include <string>
#include <utility>
#include <vector>
#include <deque>
#include <set>
using namespace std;
// }}}

// {{{ io
void newline() {cout << endl;}
template <typename T>
void display(T input){cout << input;}
template <typename T>
void put(T input){display(input); newline();}
  // }}}

const int n_max = 100000;
const int prime_number_max = 200270;
const int p_max = 100;
vector<int> prime_numbers;
int n, p;

void reserve_prime_numbers(){
   const int sievesize = prime_number_max;
   std::vector<int> sieve(prime_number_max, 1);
   sieve.reserve(prime_number_max);
   prime_numbers.reserve(prime_number_max);
   for (int i = 2; i * i < sievesize; i++)
      if (sieve[i])
         for (int j = i + i; j < sievesize; j += i)
            sieve[j] = 0;
   for (int j = 2; j < sievesize; j++)
      if (sieve[j])
        prime_numbers.push_back(j);
}

int get_index(){
  int i=0;
  for(; prime_numbers[i]<=n; i++){}
  return i;
}

int binary_search_index_rec(int s, int e){
  int i=(s+e)/2;
  if(s==e-1){return i;}
  if(prime_numbers[i]==n){return i;}
  if(prime_numbers[i]>n) return binary_search_index_rec(s, e-(e-s)/2);
  if(prime_numbers[i]<n) return binary_search_index_rec(s+(e-s)/2, e);
}

int binary_search_index(){
  return binary_search_index_rec(0, prime_numbers.size()-1);
}

int solve(){
  vector<int> prime_numbers_sum;
  int index = get_index();
  // int index = binary_search_index();
  for(int i=0+index; i<25+index; i++){
    for(int l=i; l<25+index; l++){
      int sum = prime_numbers[i] + prime_numbers[l];
        prime_numbers_sum.push_back(sum);
    }
  }
  sort(prime_numbers_sum.begin(), prime_numbers_sum.end());
  return prime_numbers_sum[p-1];
}

int main(){
  ios::sync_with_stdio(false);
  prime_numbers.reserve(prime_number_max);
  reserve_prime_numbers();
  while(cin >> n >> p && n != -1 && p != -1)
    put(solve());
}