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>

using namespace std;

int main()
{
    while (true) {
        int n, p;
        cin >> n >> p;
        if (n == -1 and p == -1) {
            break;
        }
        p--;
        int prime[100];
        int num = max(2, n + 1);
        for (int i = 0; i < 100; i++) {
            while (true) {
                bool isp = true;
                for (int j = 2; j * j <= num; j++) {
                    if (num % j == 0) {
                        isp = false;
                        break;
                    }
                }
                if (isp) {
                    prime[i] = num;
                    num++;
                    break;
                } else {
                    num++;
                }
            }
        }
        vector<int> sum;
        for (int i = 0; i < 100; i++) {
            for (int j = i; j < 100; j++) {
                sum.push_back(prime[i] + prime[j]);
            }
        }
        sort(sum.begin(), sum.end());
        cout << sum[p] << endl;
    }
    return 0;
}

C++: #include <cstdio>
#include <utility>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#define REP(i,n) for(int i=0;i<n;i++)
typedef long long ll;
using namespace std;
typedef vector<ll> vl;
typedef pair<ll,ll> pll;
typedef vector<pll> vpll;
typedef vector<string> vs;


int main() 
{
	ll a[10000];	//素数を格納する
	ll t(0);		//t番目の素数を求めたい
	while(t<10000)
	{
		if(t==0){a[t]=2;}	//最初の素数は2
		else
		{
			for(ll i =a[t-1]+1;i<101000;i++)	//前の素数+1から探索
			{
				for(ll j=0;j<t;j++)
				{
					if(i%a[j]==0){break;}	//t-1番目以前の素数で割り切れたらダメ
					if(j==(t-1)){a[t]=i;}	//t-1番目までの全てで割り切れなければ素数
				}
				if(a[t]!=0){break;}	
			}
		}
		t++;
	}
	return 0 ;
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string> 
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>
 
using namespace std;
 
int min_prime(int n);
int isprime(int n);
 
int main()
{
    int n, p;
    while(1){
        cin >> n >> p;
        if(n == -1 && p == -1) break;
        int prime_array[1000] = {0}, sum_array[50000] = {0};
        if(isprime(n)) prime_array[0] = n;
        else prime_array[0] = min_prime(n);
        for(int i = 0; i < (2 * p); i++){
            prime_array[i + 1] = min_prime(prime_array[i]);
        }
        int k = 0;
        for(int i = 0; i < (100 * p) + 1; i++){
            for(int j = i; j < (100 * p) + 1; j++){
                sum_array[k] = prime_array[i] + prime_array[j];
                k++;
            }
        }
        sort(sum_array, sum_array+k);
        cout << sum_array[p - 1] << endl;
    }
    return 0;
}
 
int min_prime(int n)
{
    while(++n){
        if(isprime(n)) break;
    }
    return n;
}
 
int isprime(int n)
{
    int ans = 0;
    if(n == 0 || n == 1) ans = 0;
    else if(n == 2) ans = 1;
    else {
        for(int i = 2; i < n; i++){
            if(i * i > n){
                ans = 1;
                break;
            }
            else if(n % i == 0){
                ans = 0;
                break;
            }
        }
    }
    return ans;
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string> 
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

int min_prime(int n);
int isprime(int n);

int main()
{
	int n, p;
	while(1){
		cin >> n >> p;
		if(n == -1 && p == -1) break;
		int prime_array[1000] = {0}, sum_array[10000] = {0};
		if(isprime(n)) prime_array[0] = n;
		else prime_array[0] = min_prime(n);
		for(int i = 0; i < p; i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < p; i++){
			for(int j = i; j < p; j++){
				sum_array[k] = prime_array[i] + prime_array[j];
				k++;
			}
		}
		sort(sum_array, sum_array+(k - 1));
		cout << sum_array[p - 1] << endl;
	}
	return 0;
}

int min_prime(int n)
{
	int i = 1;
	while(1){
		if(isprime(n + i)) return n + i;
		else i++;
	}
}

int isprime(int n)
{
	int ans;
	if(n == 0 || n == 1) ans = 0;
	else if(n == 2) ans = 1;
	else {
		for(int i = 2; i < n; i++){
			if(i * i > n) ans = 1;
			else if(n % i == 0){
				ans = 0;
				break;
			}
		}
	}
	return ans;
}