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 <algorithm>
#include <vector>
using namespace std;

bool is_prime[10000000] = {};
vector<int> get_prime() {
    for (int i = 2; i < 10000000; i++)
        is_prime[i] = true;

    for (int i = 2; i * i < 10000000; i++) {
        if (!is_prime[i]) continue;
        for(int j = i * 2; j < 10000000; j += i)
            is_prime[j] = false;
    }

    vector<int> prime_list;
    for (int i = 0; i < 10000000; i++)
        if (is_prime[i]) prime_list.push_back(i);
    return prime_list;
}

int main() {
    auto prime_list = get_prime();

    int n, p;
    while (cin >> n >> p, p > 0) {
        vector<int> x;
        for (int i = 0; i < prime_list.size() && x.size() <= p; i++) {
            if (prime_list[i] > n) {
                x.push_back(prime_list[i]);
            }
        }

        vector<int> cand;
        for (int i = 0; i < x.size(); i++)
            for (int j = i; j < x.size(); j++) {
            cand.push_back(x[i] + x[j]);
        }
        sort(cand.begin(), cand.end());
        cout << cand[p - 1] << endl;
    }
}

C++: #include <algorithm>
#include <bitset>
#include <cctype>
#include <complex>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
template<class T> inline T sqr(T x) {return x*x;}

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a)  (a).begin(),(a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define exist(s,e) ((s).find(e)!=(s).end())
#define range(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)  range(i,0,n)
#define clr(a,b) memset((a), (b) ,sizeof(a))
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi  = acos(-1.0);
const ll INF =1LL << 62;
const int inf =1 << 29;

const int nmax=300000;

bool isprime[nmax+10];

void init(){
	rep(i,nmax+10) isprime[i]=true;
	isprime[0]=isprime[1]=false;
	for(int i=2;i*i<=nmax;i++)
		if(isprime[i])
			for(int j=i*i;j<=nmax;j+=i)
				isprime[j]=false;
	return ;
}

int main(void){
	init();
	int n,p;
	while(cin >> n >> p ){
		if(n==-1&&p==-1)
			break;
			
		vi a,b;
		
		int f=0;
		for(int i=n+1;f<p;i++){
			if(isprime[i]){
				a.pb(i);
				f++;
			}
		}
		
		int na=a.size();
		rep(i,na){
			for(int j=i;j<na;j++){
				int sum=a[i]+a[j];
				b.pb(sum);
			}
		}
		sort(b.begin(),b.end());
		cout << b[p-1] << endl;
	}
	return 0;
}

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

using namespace std;

const int MAX = 1000000;
bool prime[MAX];
vector<int> V;
int N,P;

void make(){
  memset(prime,true,sizeof(prime));

  prime[0] = prime[1] = false;

  for(int i = 2; i*i < MAX; i++)
    if(prime[i])
      for(int j = 2; i*j < MAX; j++)
	prime[i*j] = false;

  for(int i = 0; i < MAX; i++)
    if(prime[i]) V.push_back(i);
 
}

void solve(){

  vector<int> M;
  vector<int>::iterator ite = upper_bound(V.begin(),V.end(),N);

  for(vector<int>::iterator i = ite; i < ite+200; i++)
    for(vector<int>::iterator j = i; j < ite+200; j++)
      M.push_back(*i+*j);

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

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

int main(){
  make();
  while(cin >> N >> P){
    if(N == -1 && P == -1) break;
    solve();
  }
  return 0;
}