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<cmath>
#include<algorithm>

using namespace std;

void eratosthenes(vector<int> &n){	
	n[0] = n[1] = 1;
	for (int i = 2;i <= 120000; i++){
		if (n[i] == 0){
			for (int j = 2; j <= (120000/i); j++){
				n[i * j] = 1;
			}

		}
	}
	return;
}

bool isPrime(int n){
	if (n < 2) return false;
	if (n == 2) return true;
	for (int i = 2; i <= sqrt(n) + 1; i++){
		if (n % i == 0) return false;
	}
	return true;
}
		
int main(){
	vector<int> era(120000);
	eratosthenes(era);
	vector<int> Primelist(120001);
	int index = 1;
	for (int i = 1; i <= era.size(); i++){
		if (era[i] == 0){
			Primelist[index] = i;
			index++;
		}
	}
	while(1){
		int n,p; cin >> n >> p;
		if (n + p == -2) break;
		index = 1;
		while(n >= Primelist[index]){
			index++;
		}
		
		vector<int> list(120000);
		for (int i = 1; i <= p; i++){
			for (int j = i; j <= p; j++){
				list[(i-1) * p + j] = Primelist[index + i - 1] + Primelist[index + j - 1];
			}
		}
		sort(list.begin(),list.end());
		index = 0;
		while(list[index] == 0){
			index++;
		}
		cout << list[index + p - 1] << endl;
		
	}

return 0;
}

C++: #include <iostream>
#include <cstdlib>
#include <string>
#include <cmath>
#include <algorithm>
using namespace std;
#define N 100000

int main(){
        int n, p, sosuu[100],count=0,sum[10000];
        string keymoji;

        cin >> n >> p;
        while(n != -1 && p != -1){
                int i=n;
                count = 0;
                if(i<2)i=2;
                for(; count<p; i++){
                        int tmp;
                        if(i==2){
                                sosuu[count]=i;
                                count++;
                                continue;
                        }
                        int m=sqrt(i);
                        for(int j=2;j<m;j++){
                                if((tmp=i%j) == 0)break;
                        }
                        if(tmp != 0){
                                sosuu[count]=i;
                                count++; 
                        }
                        
                }
                count =0;
                for(i=0; i<p; i++){
                        for(int j=i; j<p; j++){
                                sum[count]=sosuu[i]+sosuu[j];
                                count++;
                        }
                }

                sort(sum, sum+count);
                cout << sum[p-1] << endl;
                cin >> n >> p;
        }
}

C++: #include <cstdio>
#include <algorithm>
#include <vector>
using namespace std;

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

vector<int> prime;
void eratos(int N)
{
    vector<bool> isprime(N, true);
    isprime[0] = isprime[1] = false;
    
    reps(i, 2, N){
        if(isprime[i]){
            for(int j=i*2; j<N; j+=i)
                isprime[j] = false;
        }
    }
    
    rep(i, N){
        if(isprime[i])
            prime.push_back(i);
    }
}

int main()
{
    eratos(200000);
    
    int n, p;
    while(scanf("%d%d", &n, &p), n!=-1){
        vector<int> ans;
        int idx = upper_bound(prime.begin(), prime.end(), n) - prime.begin();
        
        rep(i, 200) reps(j, i, 200){
            ans.push_back(prime[i+idx] + prime[j+idx]);
        }
        
        sort(ans.begin(), ans.end());
        printf("%d\n", ans[p-1]);
    }
    
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int a[10000]={2,3},i,j,k,c=2,b[100002][101],q,w[402];
int main(){
  for(i=4;i<150000;i++){
    for(k=1,j=2;j*j<=i;j++){
      if(i%j==0){k=0;break;}
    }
    if(k)a[c++]=i;
  }k=0;
  for(i=0;i<=100000;i++){
    if(i>a[k])k++;
    for(q=0,j=k;j<k+20;j++){
      for(c=j;c<j+20;c++){
        w[q++]=a[j]+a[c];
      }
    }
    sort(w[i],w[i]+q-1);
    for(c=0;c<=100;c++)b[i][c]=w[i];
  }
  while(cin>>i>>j){
    if(i<0)break;
    cout<<b[i][j-1]<<endl;
  }
}

C++: #include<iostream>
#include<string>
#include<cmath>
#include<queue>
#include<map>
#include<set>
#include<list>
#include<iomanip>
#include<vector>
#include<functional>
#include<algorithm>
#include<cstdio>
using namespace std;
bool u[200000];
int main() {
	fill(u, u + 200000, true);
	u[0] = false; u[1] = false;
	for (int i = 2; i < 200000; i++) {
		if (u[i]) {
			int j = 2;
			while (i*j < 200000) {
				u[i*j] = false;
				j++;
			}
		}
	}
	int n, p;
	while (cin >> n >> p&&n != -1 || p != -1) {
		int a[100], f = 0;
		for (int i = n + 1; i < 200000 && f < p; i++) {
			if (u[i]) {
				a[f] = i;
				f++;
			}
		}
		int b[10000];
		f = 0;
		for (int i = 0; i < p; i++) {
			for (int j = i; j < p; j++) {
				b[f] = a[i] + a[j];
				f++;
			}
		}
		sort(b, b + f);
		cout << b[p-1] << endl;
	}
}