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;
#define ll long long
#define int long long

#define rep(i, a) for (int (i) = 0; (i) < (int) (a); (i)++)
#define reps(i, a, b) for (int (i) = (int) (a); (i) < (int) (b); (i)++)
#define rrep(i, a) for (int (i) = (int) a-1; (i) >= 0; (i)--)
#define rreps(i, a, b) for (int (i) = (int) (a)-1; (i) >= (int) (b); (i)--)
#define MP(a, b) make_pair((a), (b))
#define PB(a) push_back((a))
#define all(v) (v).begin(), (v).end()
#define PRINT(f) if((f)){cout << (TRUE__) << endl;}else{cout << FALSE__ << endl;}
#define TRUE__ "Yes"
#define FALSE__ "No"
#define PERM(v) next_permutation(all(v))
#define UNIQUE(v) sort(all(v));(v).erase(unique(all(v)), v.end())
#define CIN(type, x) type x;cin >> x

#ifdef LOCAL
#define lcout(a) cout << a;
#define lcoutln(a) cout << a << endl;
#define lcerr(a) cerr << a;
#define lcerrln(a) cerr << a << endl;
#else
#define lcout(a) 
#define lcoutln(a) 
#define lcerr(a) 
#define lcerrln(a) 
#endif

#define MAX 200000

bool gojo[MAX];
vector<int> pr;

void init()
{
	rep(i, MAX) gojo[i] = true;
	gojo[0] = gojo[1] = false;
	rep(i, MAX) {
		while (!gojo[i]) i++;
		pr.PB(i);
		for (int j = i+i; j < MAX; j += i) gojo[j] = false;
	}
}

int N, P;

signed main()
{
	init();
	cin >> N >> P;
	while (N+1) {
		N++;
		auto itr = lower_bound(all(pr), N);
		vector<int> v;
		rep(i, 22) {
			v.PB(*itr);
			itr++;
		}
		vector<int> vv;
		rep(i, 22) rep(j, 22) {
			if (i > j) continue;
			vv.PB(v[i]+v[j]);
		}
		sort(all(vv));
		cout << vv[P-1] << endl;
		cin >> N >> P;
	}
}

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

using namespace std;

bool is_prime(int n, int k = 2)
{
    if(n < k * k) { return true; }
    
    if(n % k == 0) { return false; }
    
    return is_prime(n, k + 1);
}

int main()
{
    vector<int> prime;
    
    for(int i = 2; i < 105000; i++)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
    
    int n, m;
    
    while(true)
    {
        scanf("%d", &n);
        scanf("%d", &m);
        
        if(n == -1 && m == -1) { break; }
        
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
        
        vector<int> c;
        
        for(int i = ptr; i < ptr + m; i++)
        {
            for(int j = i; j < ptr + m; j++)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
        
        sort(c.begin(), c.end());
        
        printf("%d", c[m - 1]);
    }
    
    return 0;
}

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

using namespace std;

int main()
{
    auto computePrimes = [](int n) {
        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;
            if (i > n) {
                r.push_back(i);
                if (r.size() >= 20) {
                    break;
                }
            }
            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 primes = computePrimes(n);
        priority_queue<int, vector<int>, greater<>> q;
        for (int i = 0; i < primes.size(); ++i) {
            for (int j = i; j >= 0; --j) {
                q.push(primes[i] + primes[j]);
            }
        }
        for (int i = 0; i < p - 1; ++i) {
            q.pop();
        }
        cout << q.top() << endl;
    }
}

C++: #include <vector>
#include <iostream>
#include <algorithm>
 
using namespace std;
 
bool is_prime(int n, int k = 3)
{
    if(n < k * k) { return true; }
     
    if(n % k == 0) { return false; }
     
    return is_prime(n, k + 2);
}
 
int main()
{
    vector<int> prime = {2};
     
    for(int i = 3; i < 101300; i += 2)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
     
    int n, m;
     
    while(true)
    {
        scanf("%d", &n);
        scanf("%d", &m);
         
        if(n == -1 && m == -1) { break; }
         
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
         
        vector<int> c;
         
        for(int i = ptr; i < ptr + m; i++)
        {
            for(int j = i; j < ptr + m; j++)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
         
        sort(c.begin(), c.end());
         
        printf("%d\n", c[m - 1]);
    }
     
    return 0;
}