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 <bitset>
#include <functional>
#include <iostream>
#include <queue>
#include <vector>

using namespace std;

int main()
{
    const auto primes = [] {
        vector<int> r;
        bitset<1'000'000> b;
        auto t = b;
        t.set();
        t[0] = false;
        t[1] = false;
        int i = 0;
        while (true) {
            bool done = false;
            while (!t[i]) {
                ++i;
                if (i == t.size()) {
                    done = true;
                    break;
                }
            }
            if (done) {
                break;
            }

            b[i] = true;
            r.push_back(i);
            for (int j = i; j < t.size(); j += i) {
                t[j] = false;
            }
        }
        return r;
    }();

    while (true) {
        int n, p;
        cin >> n >> p;
        if (n == -1 && p == -1) {
            return 0;
        }

        const auto s = upper_bound(begin(primes), end(primes), n);
        vector<int> q;
        for (int i = 0; i < p; ++i) {
            for (int j = i; j < p; ++j) {
                q.push_back(*(s + i) + *(s + j));
            }
        }
        sort(begin(q), end(q));
        cout << q[p - 1] << endl;
    }
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
#define MAX 200000
bool isP[MAX];
vector<int> primes;
void make_table(){
  for(int i=0;i<MAX;i++)isP[i]=true;
  isP[0]=isP[1]=false;
  for(int i=2;i*i<MAX;i++){
    if(!isP[i])continue;
    for(int j=i*i;j<MAX;j+=i)isP[j]=false;
  }
  for(int i=0;i<MAX;i++)
    if(isP[i])primes.push_back(i);
}

int N,P;
int main(){
  make_table();
  vector<int> :: iterator it;
  while(1){
    cin>>N>>P;
    if(N==-1&&P==-1)break;
    it=lower_bound(primes.begin(),primes.end(),N);
    vector<int> t,u;
    for(int i=0;i<100;i++,it++){
      t.push_back(*it);
      for(int j=0;j<=i;j++)u.push_back(t[j]+t[i]);
    }
    sort(u.begin(),u.end());
    cout<<u[P-1]<<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#define MAX 1000000
using namespace std;

int main(){
  bool a[MAX];
  vector<int> v;
  for(int i=0;i<MAX;i++) a[i] = true;
  a[0] = a[1] = false;
  for(int i=2;i<MAX;i++){
    if(a[i]){
      v.push_back(i);
      for(int j=i+i;j<MAX;j+=i) a[j] = false;
    }
  }

  int n,p;
  while(cin >> n >> p){
    if(n == -1 && p == -1) break;

    vector<int> s;
    for(int i=0;i<v.size();i++){
      if(v[i] > n){
	for(int j=i;j<i+100;j++){
	  if(j >= v.size()) break;
	  for(int k=j;k<i+100;k++){
	    if(k >= v.size()) break;
	    s.push_back(v[j]+v[k]);
	  }
	}
	break;
      }
    }

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

    cout << s[p-1] << endl;
  }
  return 0;
}

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

#define MEMZERO(x) memset(x, 0, sizeof(x))
#define MEMSET(x, y) memset(x, y, sizeof(x))

using namespace std;

const int SIZE = 101200;
bool isPrime[SIZE];
int prime[SIZE/2], pSize;
int table[5100];

int memo[10000][100];

void setPrime( void )
{
	pSize = 0;
	for(int i=2; i < SIZE; ++i) isPrime[i] = true;
	isPrime[0] = isPrime[1] = false;
	for(int i=2; i < SIZE; ++i) {
		if(!isPrime[i]) continue;
		prime[pSize++] = i;
		for(int j=i+i; j < SIZE; j+=i) {
			isPrime[j] = false;
		}
	}
}

int search_index( int num )
{
	int l=0, h = pSize;
	while(l < h) {
		int m = (l + h) / 2;
		if(prime[m] < num) l = m + 1;
		else if(prime[m] > num) h = m;
		else return (m+1);
	}
	return l;
}

int main( void )
{
	setPrime();
	for(int i=0; i < 10000; ++i) for(int j=0; j < 100; ++j) memo[i][j] = -1;
	int m, p;
	while(cin >> m >> p, m != -1 || p != -1) {
		MEMZERO(table);
		int ii = search_index(m);
		if(memo[ii][p-1] != -1) {
			cout << memo[ii][p-1] << endl;
			continue;
		}
		int count = 0;
		for(int i=0; i < 100; ++i)
			for(int j=i; j < 100; ++j) {
				table[count++] = prime[i+ii] + prime[j+ii];
			}
		sort(table, table+count);
		cout << table[p-1] << endl;
		for(int i=0; i < 100; ++i) memo[ii][i] = table[i];
	}
	return 0;
}

C++: #include<vector>
#include<algorithm>
using namespace std;
int P[300000];
int main(){
	for(int i=2;i*i<=300000;i++)if(!P[i])for(int j=i+i;j<300000;j+=i)P[j]=1;
	P[0]=P[1]=1;
	int n,p;
	while(cin>>n>>p,~p){
		vector<int> m; m.reserve(p*p);
		for(int i=n+1,c=0;c<p;i++){
			if(P[i])continue; c++;
			for(int j=i,C=0;C<p;j++)if(!P[j])m.push_back(i+j),C++;
		}
		sort(m.begin(),m.end());
		cout<<m[p-1]<<endl;
	}
	return 0;
}

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

bool isPrime(int x){
  if(x == 0 || x == 1) return false;
  for(int i = 2; i * i <= x; i++){
    if(x % i == 0){
      return false;
    }
  }
  return true;
}

int main(){
  int n, p;

  while(cin >> n >> p, n != -1 || p != -1){
    vector<int> v;

    for(int i = n + 1; v.size() != 100; i++){
      if(isPrime(i)){
        v.push_back(i);
      }
    }

    vector<int> vp;

    for(int i = 0; i < v.size(); i++){
      for(int j = i; j < v.size(); j++){
        vp.push_back(v[i] + v[j]);
      }
    }
    sort(vp.begin(), vp.end());

    cout << vp[p - 1] << endl;
  }
}