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 <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <string>
#include <stack>
#include <queue>
#include <cmath>
#include <cstdio>
#include <istream>
#include <sstream>
#include <iomanip>
using namespace std;

typedef ostringstream oss;
typedef istringstream iss;

vector<bool> Prime;
vector<int> PrimeStk;
void initPrime(long num) {
	Prime = vector<bool>(num + 1, true);
	Prime[1] = Prime[0] = false;
	long sq_num = sqrt((double)num);
	for (long i = 2; i < sq_num; i++) {
		if (Prime[i]) {
			for (long j = i + i; j <= num; j += i) {
				Prime[j] = false;
			}
		}
	}
}
void initPrimeStk(long begin) {
	PrimeStk.clear();
	for (long i = begin; i < Prime.size(); i++) {
		if (Prime[i]) {
			PrimeStk.push_back(i);
		}
	}
}

int main(void) {
	initPrime(100000 + 10000);

	int N, P;
	while (cin >> N >> P, N != -1 && P != -1) {
		initPrimeStk(N + 1);
		vector<long> stk;
		for (int i = 0; i < P; i++) {
			for (int j = i; j < P; j++) {
				stk.push_back(PrimeStk[i] + PrimeStk[j]);
			}
		}

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

		cout << stk[P - 1] << endl;
	}

	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <string>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>

using std::cin;
using std::cout;
using std::endl;
using std::setprecision;
using std::fixed;
using std::pair;
using std::make_pair;
using std::string;
using std::vector;
using std::list;
using std::map;
using std::set;
using std::queue;
using std::priority_queue;
using std::stack;

typedef vector<long> VI;
typedef vector<vector<long> > VII;
typedef vector<string> VS;
typedef pair<long, long> PII;

int main(void) {
    VI check(100300, 1);
    long size = check.size();
    check[0] = 0;
    check[1] = 0;
    for (long i = 2; i < size; i++) {
        if (check[i] == 1) {
            long j = i * 2;
            while (j < size) {
                check[j] = 0; 
                j += i;
            }
        }
    }


    long n;
    long p;
    while (cin >> n >> p) {
        if (n == -1 && p == -1) {
            break;
        }
        VI prime;
        long count = 0;
        for (long i = n + 1; i < size; i++) {
            if (check[i] == 1) {
                prime.push_back(i); 
                count++;
            }
            if (count == 100) {
                break;
            }
        }
        VI plus;
        for (long i = 0; i < prime.size(); i++) {
            for (long j = i; j < prime.size(); j++) {
                plus.push_back(prime[i] + prime[j]);
            }
        }
        sort(plus.begin(), plus.end());
        cout << plus[p - 1] << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <string>
#include <sstream>
#include <numeric>

#define rep(i, j) for(int i = 0; i < j; i++)
#define rep2(i, j) for(int i = 0; i <= j; i++)
#define all(i) i.begin(), i.end()
#define pint(i) printf("%d\n", i)

using namespace std;

vector<bool> era(1000010, true);
void makePrimeTable(int n)
{
	era[0] = false; era[1] = false;
	for (int i = 2; i <= n; i++)
	{
		if (era[i]) { for (int j = i * 2; j <= n; j += i) { era[j] = 0; } }
	}
}
int main()
{
	makePrimeTable(300000);
	int N, P; while (cin >> N >> P && N != -1)
	{
		vector<int> dat(0);
		vector<int> prm(0);
		while (1)
		{
			N++;
			if (era[N]) { prm.push_back(N);}
			if (prm.size() == P) { break; }
		}
		for (int i = 0; i < P; i++) for (int j = i; j < P; j++) { dat.push_back(prm[i] + prm[j]); }
		sort(all(dat)); 
		printf("%d\n", dat[P - 1]);
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

bool p[1010000];

void prime() {
  fill(p, p+1010000, true);
  p[0] = false;
  p[1] = false;
  for(int i = 2; i < 1010000; i++) {
    if(p[i]) {
      for(int j = 2; i*j < 1010000; j++) {
	p[i*j] = false;
      }
    }
  }
}

int search(int n, int m) {
  vector<int> a;
  int cnt = 0;
  for(int i = n+1; ; i++) {
    if(p[i]) {
      a.push_back(i+i);
      cnt++;
      if(cnt == m+10000) {
	sort(a.begin(), a.end());
	return a[m-1];
      }
      if(p[i]) {
	for(int j = n+1; j < i; j++) {
	  if(p[j]) {
	    a.push_back(i+j);
	    cnt++;
	    if(cnt == m+10000) {
	      sort(a.begin(), a.end());
	      return a[m-1];
	    }
	  }
	}
      }
    }
  }
}

int main() {
  int n, m;
  prime();

  while(cin >> n >> m, n+m != -2) {
    int ans = search(n, m);
    cout << ans << endl;
  }
}