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 <vector>
#include <queue>
#include <algorithm>
using namespace std;

const int MAX_N = 500000;

// p[i] := i 番目の素数
vector<int> p;
// is_p[i] := i が素数のとき true
bool is_p[MAX_N+1] = {false,false};

// エラトステネスのふるい
void sieve(){
	for(int i=2 ; i <= MAX_N ; i++ )
		is_p[i] = true;
	for(int i=2 ; i*i <= MAX_N ; i++ ){
		if( is_p[i] ){
			p.push_back( i );
			for(int j = i+i ; j <= MAX_N ; j += i ){
				is_p[j] = false;
			}
		}
	}
}

// N より大きい任意の2つ素数を足したものの中で P 番目に小さい数値を返す
int M(int N, int P){
	int id;
	for(int i=0 ; i < p.size() ; i++ ){
		if( p[i] > N ){
			id = i;
			break;
		}
	}
	priority_queue<int> q;
	//vector<int> v;
	for(int i = id ; i < p.size() ; i++ ){
		for(int j = i ; j < p.size() ; j++ ){
			q.push( -p[i] - p[j] );
			//v.push_back( p[i] + p[j] );
		}
	}
	//sort( v.begin() , v.end() );
	//if( P-1 >= v.size() ) return v[v.size()-1];
	//return v[P-1];
	int result;
	for(int i=0 ; i < P ; i++ ){
		result = q.top(); q.pop();
	}
	return -result;
}

int main(){
	int n,p;
	sieve();
	while( cin >> n >> p , n || p ){
		cout << M(n,p) << endl;
	}
}

C++: #include<iostream>
#include<queue>
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
using namespace std;

bool prime[7500000];

int main(){
	int n,p;
	rep(i,7500000)prime[i]=true;
	prime[0]=prime[1]=false;
	loop(i,2,3000){
		for(int j=i*2;j<7500000;j+=i)prime[j]=false;
	}
	while(1){
		cin>>n>>p;
		priority_queue<int,vector<int>,greater<int> > que;
		if(n==-1 && p==-1)break;
		loop(i,n+1,n+1000){
			loop(j,i,i+1000){
				if(prime[i] && prime[j])que.push(i+j);
			}
		}
		rep(i,p-1)que.pop();
		cout<<que.top()<<endl;
	}
	return 0;
}

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);
   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+1;}
  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());
}

C++: // AOJ 2150
#include<algorithm>
#include<iostream>
#include<vector>

const int MAX_PRIME = 150000;

bool used[MAX_PRIME];
std::vector<int> primes;

int n, p;

void sieve( int n )
{
	used[0] = used[1] = true;
	for( int i = 2; i <= n; ++i )
	{
		if( !used[i] )
		{
			primes.push_back( i );
			for( int j = i; j <= n; j += i )
				used[j] = true;
		}
	}

	return;
}

int main()
{
	sieve( MAX_PRIME );

	while( std::cin >> n >> p, ~( n & p ) )
	{
		int idx = std::upper_bound( primes.begin(), primes.end(), n ) - primes.begin();

		std::vector<int> sum;
		for( int i = idx; i < idx + p && i < primes.size(); ++i )
			for( int j = i; j < idx + p && j < primes.size(); ++j )
				sum.push_back( primes[i] + primes[j] );

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

	return 0;
}

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

#define MAX_N 5000000

using namespace std;

vector<int>  primes;
vector<bool> is_prime;

void Init()
{
  is_prime.resize(MAX_N + 1, true);
  for (int i = 2; i <= MAX_N; i++)  {
    if (is_prime[i]) {
      primes.push_back(i);
      for (int j = i * 2; j <= MAX_N; j += i) {
        is_prime[j] = false;
      }
    }
  }
}

int Func(int N, int P)
{
  vector<int> vi;
  int offset;
  for (offset = 0; offset < primes.size(); offset++) 
    if (primes[offset] > N)
      break;

  for (int i = 0; i < P; i++)
    for (int j = i; j < P; j++) {
      vi.push_back(primes[i + offset] + primes[j + offset]);
    }

  sort(vi.begin(), vi.end());
  return vi[P - 1];
}

int main()
{
  Init();
  int N, P;
  while (cin >> N >> P && N != -1 && P != -1) {
    cout << Func(N, P) << endl;
  }
}