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 <iomanip>
#include <sstream>
#include <stdio.h>
#include <list>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <algorithm>
#include <math.h>
#include <utility>
#include <string>
#include <ctype.h>
#include <cstring>
#include <cstdio>
#include <sstream>
#include <functional>

using namespace std;

#define FOR(i,k,n) for(int i = (k); i < (n); i++)
#define REP(i,n) FOR(i,0,n)
#define INF 114514810
#define ll long long
#define SORT(v) sort((v).begin(),(v).end())
//#define scanf scanf_s

int main()
{
	bool prime[200000];
	memset(prime, true, sizeof(prime));
	prime[0] = prime[1] = false;
	for (int i = 2; i*i < 200000; i++)
	{
		if (prime[i] == true)
		{
			for (int j = 2; i*j < 200000; j++)
			{
				prime[i*j] = false;
			}
		}
	}

	int n, p;
	while (cin >> n >> p)
	{
		if (n == -1) break;
		vector<int> v, s;

		for (int i = n; v.size() < 100; ++i)
		{
			if (prime[i] == true) v.push_back(i);
		}
		REP(i, 100)for (int j = i; j < 100; j++)
		{
			s.push_back(v[i] + v[j]);
		}
		SORT(s);
		cout << s[p - 1] << endl;

	}
	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 < (2 * p) + 1; i++){
			for(int j = i; j < (2 * 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 <iostream>
#include <vector>
#include <algorithm>

#define N 1000000

using namespace std;

vector<int> primes;

void init_primes() {
    for (int p=2; p<N; p++) {
        bool is_prime = true;
        for (vector<int>::iterator iter=primes.begin(); iter!=primes.end(); iter++) {
            if (p%(*iter) == 0) {
                is_prime = false;
                break;
            }
            if ((*iter)*(*iter) > p) {
                break;
            }
        }
        if (is_prime) {
            primes.push_back(p);
        }
    }
}

int matsuzaki(int n, int p) {
    vector<int> candidates;
    vector<int>::iterator iter1, iter2;
    iter1 = upper_bound(primes.begin(), primes.end(), n);
    for (int i=0; i<p && iter1!=primes.end(); i++, iter1++) {
        iter2 = iter1;
        for (int j=0; j<p && iter2!=primes.end(); j++, iter2++) {
            candidates.push_back((*iter1)+(*iter2));
        }
    }
    sort(candidates.begin(), candidates.end());
    return candidates[p-1];
}

int main() {
    int n, p;
    init_primes();
    while (true) {
        cin >> n >> p;
        if (n < 0) {
            return 0;
        }
        cout << matsuzaki(n, p) << endl;
    }
}