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 N_MAX 110000

void dump(vector<int>& v,int n){

	  for(int i=0; i<min(n,(int)v.size()); i++)
			cout << v[i] <<  " ";
	  cout << endl;
}

int main(){
	  
	  bool is_pri[N_MAX] = {false};
	  vector<int> pri; 

	  for(int i=2; i<N_MAX; i++) is_pri[i] = true;

	  for(int i=2; i<N_MAX; i++){
			if( is_pri[i] ) {
				  for(int j=2; j*i<N_MAX; j++)
						is_pri[i*j] = false;
				  pri.push_back(i);
			}
	  }

//	  dump(pri,100);
//	  cout << pri.size() << endl;
	  int N,P;
	  while(cin >> N >> P){
			if(N==-1) break;

			int i = upper_bound(pri.begin(),pri.end(),N) - pri.begin();
//			cout << pri[i] << endl;
			vector<int> ans(P,INT_MAX);
			
			for(int j=i; j<pri.size(); j++){
				  for(int k=j; k<pri.size(); k++){
						ans.push_back(pri[j] + pri[k]);
						sort(ans.begin(),ans.end());
						ans.pop_back();
//						dump(ans,1000);
				  }
			}
			cout << ans[P-1] << endl;
			

	  }

}

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[10000] = {0};
		if(isprime(n)) prime_array[0] = n;
		else prime_array[0] = min_prime(n);
		for(int i = 0; i < 100; i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < 30; i++){
			for(int j = i; j < 30; 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)
{
	int i = 1;
	while(1){
		if(isprime(n + i)) return n + i;
		else i++;
	}
}

int isprime(int n)
{
	int ans;
	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;
			else if(n % i == 0){
				ans = 0;
				break;
			}
		}
	}
	return ans;
}

C++: #include <iostream>
#include <vector>
using namespace std;
const int MAX = 1e6;

bool prime[MAX];

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

int main(){
  int n,p;

  is_prime();

  while(true){
    cin >> n >> p;
    if(n == -1 && p == -1) break;

    vector<int> v;
    for(int i = n+1 ; i < n+500 ; i++){
      if(prime[i]) v.push_back(i);
    }

    vector<int> ans;
    for(int i = 0 ; i < (int)v.size() ; i++){
      for(int j = i ; j < (int)v.size() ; j++){
	ans.push_back(v[i]+v[j]);
      }
    }
    sort(ans.begin(),ans.end());

    cout << ans[p-1] << endl;
  }  

  return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef long long LL;
typedef vector<int>    VI;
typedef vector<bool>   VB;
typedef vector<string> VS;

#define MP make_pair
#define PB push_back
#define ALL(x)  (x).begin(),(x).end()
#define rep(i, N)  for (int i = 0; i < (int)(N); i++)
#define REP(i, init, N)  for (int i = (init); i < (int)(N); i++)
#define DUMP( x ) cerr << #x << " = " << ( x ) << endl

vector<bool> isPrimes(int n) {
	vector<bool> res(n, true);
	res[0] = res[1] = false;
	for (int i = 2;i < sqrt(n);i++) {
		if (res[i]) {
			for (int j = 0;i * (j + 2) < n;j++) {
				res[i * (j + 2)] = false;
			}
		}
	}
	return res;
}

vector<int> primes(int n) {
	vector<bool> is_primes = isPrimes(n);
	vector<int> res;
	for (int i = 2;i < n;i++) {
		if (is_primes[i]) {
			res.push_back(i);
		}
	}
	return res;
}

VI ps;
VI qs;
int n, p;

int main(void) {
	ps = primes(100000 * 2);
	while (1) {
		qs.clear();
		cin >> n >> p;
		if (n == -1 && p == -1) break;
		int idx = 0;
		rep (i, ps.size()) {
			if (n < ps[i]) {
				idx = i;
				break;
			}
		}
		REP (i, idx, p + idx) {
			REP (j, i, p + i) {
				qs.PB(ps[i] + ps[j]);
			}
		}
		sort(ALL(qs));
		cout << qs[p - 1] << endl;
	}
    return 0;
}