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 <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
using namespace std;

#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<pii, int> ppi;

#define INF 1000000000
#define MAX 200000

// sieve of Eratosthenes (prime num)
bool p[MAX+1]; //prime number=true
void prime(int n){
  rep(i,n+1) p[i]=true;
  p[0]=p[1]=false;
  for(int i=2;i<=n;i++){
    if(p[i]){
      for(int j=i*2; j<=n; j+=i){
	p[j]=false;
      }
    }
  }
}


int main(){
  prime(MAX);
  int n,P;
  while(scanf("%d %d", &n, &P), n^P){
    int nums[100];
    vector<int> adds;

    // take P prime number bigger than n
    int cnt=0, idx=n+1;
    while(cnt<P){
      if(p[idx]){
	nums[cnt]=idx;
	cnt++;
	rep(i,cnt){
	  adds.pb(nums[i]+idx);
	}
      }
      idx++;
    }

    sort(all(adds));

    cout << adds[P-1] << endl;

  }
  return 0;
}

C++: #include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<cstdio>
#include<sstream>
#include<iomanip>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mp make_pair
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)
using namespace std;
//kaewasuretyuui
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef pair<int,pii> pip;
typedef vector<pip>vip;
const double PI=acos(-1);
const double EPS=1e-8;
const int inf=1e8;
#define MAX 300000
int main(){
	bool sosu[MAX]={1,1};
	for(int i=2;i*i<=MAX;i++)if(sosu[i]==0)
	for(int j=i*2;j<MAX;j+=i)sosu[j]=1;
	//sosu[i]=0 -> i is sosu
	
	int a,b;
	while(cin>>a>>b,a+1){
		vi sos;
		int t=a+1;
		while(sos.size()!=b){
			if(sosu[t]==0)sos.pb(t);
			t++;
		}
		vi sum;
		rep(i,b)loop(j,i,b)sum.pb(sos[i]+sos[j]);
		sort(all(sum));
		cout<<sum[b-1]<<endl;
	}
	
}

C++: #include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repp(i, n) rep(i, 0, n)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define int long long
using namespace std;

const int MAX_N = 1000000;

vector<int> prime;
bool is_prime[MAX_N + 1];
void sieve(int n){
    for(int i = 0; i <= n; i++) is_prime[i] = true;
    is_prime[0] = is_prime[1] = false;
    for(int i = 2; i <= n; i++){
        if(is_prime[i]){
            prime.push_back(i);
            for(int j = 2*i; j <= n; j += i) is_prime[j] = false;
        }
    }
}

signed main(){
    sieve(MAX_N);
    //rep(i,0 , 100) cout << prime[i] << endl;
    int n, p;
    while(1){
        cin >> n >> p;
        if(n == -1 && p == -1) break;
        vector<int> sum;
        int ind = upper_bound(all(prime), n) - prime.begin();
        //cout << ind << endl;
        rep(i ,0 ,p){
            rep(j, i, p){
                int tmp = prime[ind + i] + prime[ind + j];
                //cout << tmp << endl;                
                sum.push_back(tmp);
            }
        }
        sort(all(sum));
        cout << sum[p - 1] << endl;
    }
}

C++: #include <iostream>
using namespace std;
bool prime[200005] = {true};

void init(void){
    prime[0] = false, prime[1] = false;
    for(int i = 2 ; i < 1000 ; i++){
        if(prime[i] == true){
            for(int k = 2 ; i * k < 200005 ; k++){
                prime[i * k] = false;
            }
        }
    }
}

int main(void){
    init();
    for(;;){
        int N, P;
        cin >> N >> P;
        if(N == -1 && P == -1){return 0;}
        int p[15];
        int ptr=0;
        for(int i = N + 1 ; ptr<15 ; i++){
            if(prime[i]){p[ptr] = i; ptr++;}
        }
        int sum[120]; ptr=0;
        for(int i = 0 ; i < 15 ; i++){
            for(int j = i ; j < 15 ; j++){
                sum[ptr] = prime[i] + prime[j]; ptr++;
            }
        }
        for(int i = 0 ; i < 15 ; i++){
            for(int j = i+1 ; j < 15 ; j++){
                if(sum[i] < sum[j]){
                    int temp = sum[i];
                    sum[i] = sum[j];
                    sum[j] = temp;
                }
            }
        }
        cout << sum[P-1] << endl;
    }
}