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>
#define pb push_back
#define all(v) v.begin(),v.end()
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
#define MAXBOOL 7000000
using namespace std;

int main(){
	int n,p;
	vector<int> prime;
	bool check[MAXBOOL];
	while(cin>>n>>p,n!=-1||p!=-1){
		prime.clear();
		fill(check,check+MAXBOOL,true);
		check[0]=check[1]=false;
		loop(i,2,1000){
			for(int j=i*2;j<MAXBOOL;j+=i){
				check[j]=false;
			}
		}
		int cnt=0;
		while(prime.size()<500){
			if(check[n+1+cnt])prime.pb(n+1+cnt);
			cnt++;
		}
		vector<int> ans;
		rep(i,prime.size()){
			loop(j,i,prime.size()){
				ans.pb(prime[i]+prime[j]);
			}
		}
		sort(all(ans));
		cout<<ans[p-1]<<endl;
	}
	return 0;
}

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 < (p * 2); i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < p; i++){
			for(int j = i; j < p; 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 <stdio.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <cctype>

#include <iostream>
#include <vector>
#include <deque>
#include <queue>
#include <map>
#include <algorithm>

using namespace std;

#define rep(i, n) for(int i = 0; i < n; i++)

typedef pair<int ,int> P;

vector<int> primes;

void init_prime() {
    while (primes.size() < 200000) {
        if (primes.size() == 0) {
            primes.push_back(2);
            continue;
        }
        for (int n=primes[primes.size()-1]+1; true; n++) {
            bool is_prime = true;
            for (int i=0; i<(int)primes.size(); i++) {
                if (n%primes[i] == 0) {
                    is_prime = false;
                    break;
                }
                if (primes[i]*primes[i] > n) {
                    break;
                }
            }
            if (is_prime) {
                primes.push_back(n);
                break;
            }
        }
    }
}

int matsuzaki(int n, int p) {
    int least;
    vector<int> m;
    for (least=0; primes[least]<=n; least++);
    for (int bigger=least; bigger<least+p; bigger++) {
        for (int smaller=least; smaller<=bigger; smaller++) {
            m.push_back(primes[smaller]+primes[bigger]);
        }
    }
    sort(m.begin(), m.end());
    return m[p-1];
}

int main()
{
    int n, p;
    init_prime();
    while (true) {
        cin >> n >> p;
        if (n < 0) {
            break;
        }
        cout << matsuzaki(n, p) << endl;
    }
    return 0;
}

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

#define int long long

bool isprime[200000];

signed main() {
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  fill_n(isprime, 200000, true);
  isprime[0] = isprime[1] = false;  
  for ( int i = 2; i*i < 200000; i++ ) {    
    for ( int j = 2; i*j < 200000; j++ ) {
      isprime[i*j] = false;      
    }
  }

  int N, P;
  while ( cin >> N >> P, N != -1 ) {
    int cnt = 0;
    vector<int> p;    
    for ( int i = N+1; i < 200000; i++ ) {
      if ( isprime[i] ) {
	p.push_back(i);
	// cout << i << endl;
	if ( cnt++ >= 100 ) break;
      }
    }

    // cout << p.size() << endl;

    vector<int> ans;
    for ( int i = 0; i < (int)p.size(); i++ ) {
      for ( int j = i; j < (int)p.size(); j++ ) {
	ans.push_back(p[i]+p[j]);	
      }
    }

    sort(ans.begin(), ans.end());
    // for ( int i = 0; i < 10; i++ ) cout << ans[i] << " ";
    cout << ans[P-1] << endl;    
  }
  
  return 0;
}