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 <string>
#include <algorithm>
#include <vector>
#include <utility>
#include <cstring>
using namespace std;

#define rep(i,n) for(int i=0; i<n; i++)
typedef long long ll;

const int MAX = 1000000;
bool prime[MAX];

int main() {
	prime[0] = prime[1] = true;
	for(int i=2; i*i<MAX; i++) {
		if(!prime[i]) {
			for(int j=i+i; j<MAX; j+=i) {
				prime[j] = true;
			}
		}
	}
	vector<int> primes;
	rep(i,MAX) {
		if(!prime[i]) {
			primes.push_back(i);
		}
	}

	int n, p;
	while(cin>>n>>p, n!=-1&&p!=-1) {
		int index = 0;
		while(primes[index]<=n) index++;
		vector<int> nums;
		int lim = min((int)primes.size(), index+p);
		for(int i=index; i<lim; i++) {
			for(int j=i; j<lim; j++) {
				nums.push_back(primes[i]+primes[j]);
			}
		}
		sort( nums.begin(), nums.end() );
		cout << nums[p-1] << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
    bool nonprime[120000] = {};
    vector<int> prime;
    for(int i = 2; i < 120000; i++){
        if(!nonprime[i]){
            prime.push_back(i);
            for(int j = i+i; j < 120000; j += i)    nonprime[j] = true;
        }
    }

    int n, p;

    while(cin >> n >> p, n+p != -2){
        vector<int> use;
        auto it = upper_bound(prime.begin(), prime.end(), n);
        for(int i = 0; i < 100; i++) use.push_back(*it), it++;

        vector<int> sum;
        for(int i = 0; i < 100; i++) for(int j = i; j < 100; j++) sum.push_back(use[i]+use[j]);
        sort(sum.begin(), sum.end());

        cout << sum[p-1] << endl;
    }
    return 0;
}

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

using namespace std;

int main(void)
{
	int n,p;
	int check;

	int i1,i2;

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

		vector<int> sosu;

		i1=n+1;
		if(i1==1 || i1==2) {
			sosu.push_back(2);
			i1=3;
		}

		while(sosu.size()<=p){
			
			check=0;

			
			for(i2=2;i2*i2<=i1;i2++){
				if(i1%i2==0){
					check=1;
					break;
				}
			}

			if(check==0) sosu.push_back(i1);
			i1++;

		}

		vector<int> matsuzaki;

		for(i1=0;i1<sosu.size();i1++){
			for(i2=i1;i2<sosu.size();i2++){
				matsuzaki.push_back(sosu[i1]+sosu[i2]);
			}
		}

		sort(matsuzaki.begin(), matsuzaki.end());

		cout << matsuzaki[p-1] << endl;

	}
	return 0;


}

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

#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;
  }
}

C++: #include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;

const int MAX = 1000001;
bool p[MAX];
vector<int> pn;

void f(){
    for(int i=0 ; i<MAX ; i++){
        p[i] = (i<=1)? false : true ;
    }
    for(int i=2 ; i <= sqrt(MAX)+1 ; i++){
        if( p[i] ){
            for(int j=i*2 ; j<MAX ; j+=i){
                p[j] = false;
            }
        }
    }
	for(int i=0 ; i<MAX ; i++){
        if( p[i] ){
			pn.push_back( i );
		}
    }
}

int M(int n, int p){
	int i_=0;
	vector<int> vc;
	for( ; i_ < (int)pn.size() && pn[i_] < n; i_++ );
	
	for(int i=i_ ; i < i_+100 ; i++ ){
		for(int j=i ; j < i_+100 ; j++ ){
			if( i >= (int)pn.size() || j >= (int)pn.size() ) continue;
			//if( !count(vc.begin(),vc.end(),pn[i]+pn[j]) )
				vc.push_back( pn[i]+pn[j] );
		}
	}
	sort( vc.begin() , vc.end() );
	return vc[p-1];
}

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

C++: #include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
using namespace std;

const int MAX_N = 200000;

// 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 pi[100];
	priority_queue<int, vector<int>, greater<int> > q;
	int pn = 0;
	for(int i = N+1 ; pn < P ; i++ ){
		if( is_p[i] ){
			pi[pn++] = i;
		}
	}
	for(int i=0 ; i < P ; i++ ){
		for(int j=i ; j < P ; j++ ){
			q.push( pi[i] + pi[j] );
		}
	}
	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 != -1 ){
		cout << M(n,p) << endl;
	}
}