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 <set>
using namespace std;

const int MAX_N = 200000;
const int MAX_PRIMES_SIZE = 20000;
int primes[MAX_PRIMES_SIZE];
int primesSize;
const int P_LOOP_SIZE = 100;

void setPrimes() {
    fill_n(primes, MAX_PRIMES_SIZE, 0);
    primes[0] = 2;
    primesSize = 1;
    for (int i = 3; i < MAX_N; i += 2) {
        bool isPrime = true;
        for (int j = 0; j < primesSize; j++) {
            if (i % primes[j] == 0) {
                isPrime = false;
                break;
            }
        }
        if (isPrime == true) {
            primes[primesSize++] = i;
        }
    }
}

int main() {
    setPrimes();
    while (true) {
        int n, p;
        cin >> n >> p;
        if (n == -1 && p == -1) {
            break;
        }
        int *start;
        for (int i = 0; i < MAX_PRIMES_SIZE; i++) {
            if (primes[i] > n) {
                start = primes + i;
                break;
            }
        }
        multiset<int> pSet;
        for (int i = 0; i < P_LOOP_SIZE; i++) {
            for (int j = i; j < P_LOOP_SIZE; j++) {
                pSet.insert(*(start + i) + *(start + j));
            }
        }
        int i = 0;
        for (set<int>::iterator it = pSet.begin(); it != pSet.end(); it++) {
            if (i == p - 1) {
                cout << *it << endl;
                break;
            }
            i++;
        }
    }
}

C++: #include<bits/stdc++.h>
#define range(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,b) range(i,0,b)
#define pb(a) push_back(a)
#define all(a) (a).begin(), (a).end()
#define debug(x) cout << "debug " << x << endl;
using namespace std;

int main(){
    int n,p;
    bool prime[200001] = {1,1,0};
    vector<int> PrimeNumber;
    vector<int> number;
    vector<int>::iterator it;
    vector<int>::iterator cpit;

    rep(i,200000){
        if(!prime[i]){
            for(int j = i + i; j < 200000; j+=i){
                prime[j] = 1;
            }
        }
    }
    rep(i,200000) if(!prime[i]) PrimeNumber.pb(i);

    while(cin >> n >> p, n != -1 || p != -1){
        for(it = PrimeNumber.begin(); it != PrimeNumber.end(); it++){
            if(*it > n) break;
        }
        //rep(i,15) cout << *(it + i) << endl;
        for(int i = 0; i < 30; i++){
            cpit = it;
            for(int j = i; j < 30; j++){
                number.pb(*it + *cpit);
                cpit++;
            }
            it++;
        }
        sort(all(number));
        //rep(i,101) cout << number[i] << endl;
        //debug(number.size());
        cout << number[p - 1] << endl;
        number.clear();
    }
}

C++: #include <iostream>
#include <sstream>
#include <fstream>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cmath>
using namespace std;

typedef long long Int;

const int SQRTN = 1<<16; // upperbound of sqrt(H)
vector<Int> segmentSieve(Int L, Int H) {
  static int p[SQRTN], lookup = 0;
  if (!lookup) {
    for (int i = 2; i < SQRTN; ++i) p[i] = i;
    for (int i = 2; i*i < SQRTN; ++i)
      if (p[i])
        for (int j = i*i; j < SQRTN; j += i)
          p[j] = 0;
    remove(p, p+SQRTN, 0);
    lookup = 1;
  }
  vector<Int> table(H - L);
  for (Int i = L; i < H; ++i) table[i - L] = i;
  for (int i = 0, j; p[i] * p[i] < H; ++i) { // O( \sqrt(H) )
    if (p[i] >= L) j = p[i] * p[i];
    else if (L % p[i] == 0) j = L;
    else                    j = L - (L % p[i]) + p[i];
    for (; j < H; j += p[i]) table[j-L] = 0;
  }
  return table;
}

int main() {
    int n, p;
    while ( cin >> n >> p ) {
        if ( n == -1 && p == -1 ) break;
        if ( n < 2 ) n = 2;
        vector <Int> T = segmentSieve( n, n+1000 );
        vector <Int> P;
        for ( int i = 0; i < (int)T.size(); i++ ) {
            if ( T[i] != 0 ) {
                P.push_back( n+i );
            }
        }
        int N = P.size();
        vector <Int> X;
        for ( int i = 0; i < min( 100, N ); i++ ) {
            for ( int j = i; j < min( 100, N ); j++ ) {
                X.push_back( P[i] + P[j] );
            }
        }
        sort( X.begin(), X.end() );
        cout << X[p-1] << endl;
    }
    return 0;
}