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 <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>

using namespace std;
#define REP(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define RREP(i, a) for(int (i) = (a) - 1; (i) >= 0; (i)--)
#define FORR(i, a, b) for(int (i) = (a) - 1; (i) >= (b); (i)--)
#define DEBUG(C) cerr << #C << " = " << C << endl;
using LL = long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<LL>;
using VVL = vector<VL>;
using VD = vector<double>;
using VVD = vector<VD>;
using PII = pair<int, int>;
using PDD = pair<double, double>;
using PLL = pair<LL, LL>;
using VPII = vector<PII>;
#define ALL(a) begin((a)), end((a))
#define RALL(a) rbegin((a)), rend((a))
#define SORT(a) sort(ALL((a)))
#define RSORT(a) sort(RALL((a)))
#define REVERSE(a) reverse(ALL((a)))
#define MP make_pair
#define FORE(a, b) for (auto &&a : (b))
#define FIND(s, e) ((s).find(e) != (s).end())
#define EB emplace_back

const int INF = 1e9;
const int MOD = INF + 7;
const LL LLINF = 1e18;

vector<int> sieve_of_eratosthenes(int n) {
    vector<bool> is(n + 1, true);
    vector<int> res;
    is[0] = false;
    is[1] = false;
    for (int i = 2; i <= n; i++) if (is[i]) {
        res.emplace_back(i);
        for (int j = i * 2; j <= n; j += i) {
            is[j] = false;
        }
    }
    return res;
}
VI primes;
void solve(int N, int P) {
    int start;
    REP(i, primes.size()) {
        if (primes[i] > N) {
            start = i;break;
        }
    }
    set<int> se;
    FOR(i, start, primes.size()) {
        FOR(j, i, primes.size()) {
            se.insert(primes[i] + primes[j]);
            if (se.size() >= P) {
                break;
            }
        }
    }
    int cnt = 0;
    FORE(e, se) {
        cnt++;
        if (cnt == P) {
            cout << e << endl;
            break;
        }
    }
    return;
}

signed main(void) {
    int n, m, p, a, b, c, x, y, z, q;
    string s;
    bool f = false;
    primes = sieve_of_eratosthenes(200000);
    while (cin >> n >> m, n != -1) {
        solve(n, m);
        //return 0;
    }
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <numeric>
#include <complex>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <array>
#include <unordered_map>
#include <unordered_set>

using namespace std;

#define all(c) begin(c), end(c)
#define dump(c) cerr << "> " << #c << " = " << (c) << endl
#define tr(i, c) for (auto i = (c).begin(); i != (c).end(); i++)
#define REP(i, a, b) for (int i = a; i < (int)(b); i++)
#define rep(i, n) REP(i, 0, n)
#define mp make_pair
#define pb push_back

typedef long long ll;
typedef vector<int> vi;
typedef vector<double> vd;
typedef pair<int,int> pii;

const int INF = 1 << 29;
const double EPS = 1e-10;


int main() {
  array<bool, 1000000> is_p;
  fill(all(is_p), true);
  is_p[0] = is_p[1] = false;
  for (int i = 2; i * i < (int)is_p.size(); i++) if (is_p[i])
    for(int j = i * 2; j < (int)is_p.size(); j += i) is_p[j] = false;
  
  vi prime;
  rep(i, is_p.size()) if (is_p[i]) prime.pb(i);


  for (int N, P; cin >> N >> P, N + P != -2; ) {
    int p = 0;
    while(prime[p] <= N) p++;

    priority_queue<int, vi, greater<int>> que;

    rep(i, 100) rep(j, 100) que.push(prime[p + i] + prime[p + i + j]);

    rep(i, P - 1) que.pop();
    
    cout << que.top() << endl;



  }
  
  
  return 0;
}