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 <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;
                int tmp=sqrt(n);
                if(i<2)i=2;
                for(; count<p; i++){
                        int tmp;
                        if(i==2){
                                sosuu[count]=i;
                                count++;
                                continue;
                        }
                        for(int j=2;j<sqrt(i)+1;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<iostream>
#include<vector>
#include<algorithm>
typedef unsigned int  ui;
using namespace std;
const ui MAXP = 103000;
vector<int> p;

void initPrime(){
  p.push_back(2);
  bool isPrime;
  for(int i = 3;;i+=2){
    isPrime = true;
    for(ui j = 0;j < p.size();j++){
      if(i%p[j] == 0){
	isPrime = false;
	break;
      }
    }
    if(isPrime == true){
      p.push_back(i);
      if(i >= MAXP)break;
    }
  }
}



int M(int N,int P){
  //beginはN以上の最初に現れる素数
  vector<int>::const_iterator begin = upper_bound(p.begin(),p.end(),N);

  vector<int> sum;
  for(int i = 0;i <= P;i++){
    for(int j = i;j <= P;j++){
      sum.push_back(*(begin+i) + *(begin+j) );
    }
  }
  sort(sum.begin(),sum.end());
  return sum[P-1];
}

int main(){
  int N,P;
  initPrime();
  while(cin >> N >> P && N+P >= 0){
    cout << M(N,P) << endl;
  }
  return 0;
}

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

C++: //Name: Matsuzaki Number
//Level: 2
//Category: 素数
//Note:

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

const int MAX_PRIME = 200000;
vector<int> primes;
bool is_prime[MAX_PRIME+1];

void init() {
    fill_n(is_prime, MAX_PRIME+1, true);
    is_prime[0] = is_prime[1] = false;
    for(int i = 2; i <= MAX_PRIME; ++i) {
        if(is_prime[i]) {
            primes.push_back(i);
            for(long long j = (long long)i*i; j <= MAX_PRIME; j += i) {
                is_prime[j] = false;
            }
        }
    }
}

bool solve() {
    int N, P;
    cin >> N >> P;
    if(!N && !P) return false;

    vector<int>::iterator first = upper_bound(primes.begin(), primes.end(), N);
    vector<int> nums;
    const int start = distance(primes.begin(), first);
    for(int i = start; i < start+100; ++i) {
        for(int j = i; j < start+100; ++j) {
            nums.push_back(primes[i]+primes[j]);
        }
    }
    sort(nums.begin(), nums.end());
    cout << nums[P-1] << endl;
    return true;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(0);

    init();
    for(int case_num = 1; solve(); ++case_num) ;
    return 0;
}

C++: #include<bits/stdc++.h>
#define INF 200000
using namespace std;

bool sosuu[INF];
int main() {
	memset(sosuu, true, sizeof(sosuu));
	sosuu[0] = sosuu[1] = false;
	for (int a = 2; a < INF; a++) {
		if (sosuu[a]) {
			for (int b = a * 2; b < INF; b+=a)sosuu[b] = false;
		}
	}
	int x, y;
	while (cin >> x >> y, (x+1)|(y+1)) {
		int s[20000];
		fill(s, s + (y+1)*(y+1), 1 << 29);
		int sum = 0, l = 0;
		for (int z = x+1; l <= y; z++) {
			if (sosuu[z]) {
				l++;
				int r = l;
				for (int i = z; r <= y; i++) {
					if (sosuu[i]) {
						r++;
						s[sum] = z + i;
						sum++;
					}
				}
			}
		}
		sort(s, s + (y + 1)*(y + 1));
		cout << s[y-1] << endl;
	}
}