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<algorithm>
#define pb push_back 
#include<vector>
#define all(c) c.begin(), c.end()
using namespace std;
int N=200000;
int main(){
  int n,p;
  vector<int> pr(200000,1);
  pr[0]=0;
  pr[1]=0;
  vector<int> prime;
  for(int i=0;i*i<N;i++){
    if(pr[i]){
      for(int j=i*2;j<N;j+=i){
	pr[j]=0;
      }
    }
  }
  for(int i=0;i<N;i++)
    if(pr[i])
      prime.pb(i);
  /*for(int i=0;i<(int)prime.size();i++)
    cout<<prime[i]<<endl;
  */
  while(cin>>n>>p,n!=-1||p!=-1){
    vector<int> buf,plus;
    int cnt=0;
    for(int i=0;i<prime.size()&&cnt<p;i++){
      if(prime[i]>n){
	cnt++;
	buf.pb(prime[i]);
      }
    }
    for(int i=0;i<p;i++){
      for(int j=i;j<p;j++){
	plus.pb(buf[i]+buf[j]);
      }
    }
    sort(all(plus));
    /* for(int i=0;i<plus.size();i++)
      cout<<plus[i]<<endl;
    */
    cout<<plus[p-1]<<endl;
  }

  return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;
int prime[200000];
bool is_prime[200000];
int sieve(int n);
vector<int> prime_prime;
int main(){
  sieve(200000);
  int n,p;
  int count=0;
  while(cin>>n>>p){
    count=0;
    prime_prime.clear();
    if(n==-1 && p==-1)break;
    while(prime[count]<=n)count++;
    for(int i=count;i<p+count;i++)
      for(int j=i;j<p+count;j++)
	prime_prime.push_back(prime[i]+prime[j]);
    sort(prime_prime.begin(),prime_prime.end());
    //for(int i=0;i<num;i++)cout<<prime_prime[i]<<endl;    
    cout<<prime_prime[p-1]<<endl;
  }
  return 0;
}

int sieve(int n){
  int p = 0;
  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[p++]=i;
      for(int j=2*i;j<=n;j+=i)is_prime[j]=false;
    }
  }
  return p;
}

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 < (2 * p); i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < (2 * p) + 1; i++){
			for(int j = i; j < (2 * p) + 1; 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)
{
	while(++n){
		if(isprime(n)) break;
	}
	return n;
}

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

using namespace std;

int Mfunc(int num,int p);
vector<int> primesearch(int num);
bool isprime(int num);

vector<int> ans;

int main(){
	while(1){
		int n,p;
		cin >> n >> p;
		if(n == -1 && p == -1)break;
		int tans = Mfunc(n,p);
		ans.push_back(tans);
	}
	for(int i= 0;i < ans.size();i++) cout << ans[i] << endl;
}

int Mfunc(int num,int p){
	vector<int> pri = primesearch(num);
	vector<int> M;
	for(int i = 0;i < pri.size();i++){
		for(int j = 0;j <= i;j++){
			int tm = pri[i] + pri[j];
			M.push_back(tm);
		}
	}
	sort(M.begin(),M.end());
	return M[p-1];
}

vector<int> primesearch(int num){
	num++;
	vector<int> primes;
	while(primes.size() < 100){
		if(isprime(num)) primes.push_back(num);
		num++;
	}
	return primes;
}

bool isprime(int num){
	if(num < 2) return false;
	for(int i = 2;i < num;i++){
		if(i*i > num) break;
		if(num % i == 0) return false;
	}
	return true;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define Max 500000
vector<int> prim;
vector<bool> res(Max+1,true);
void aris(int n){
res[0]=res[1]=false;
	for(int i=2;i<=n;i++){
		if(res[i]){
			prim.push_back(i);
			int k=2;
			while(i*k<=n){
			res[i*k]=false;
			k++;
			}
		}
	}
	return ;
}

int main(){
int n,p;

aris(Max);
while(1){
	cin>>n>>p;
	if(n==-1)break;
	vector<int> tmp,ans;
auto now =upper_bound(prim.begin(),prim.end(),n);
for(int i=0;i<=p;i++){
tmp.push_back(*now);
	for(int j=0;j<=i;j++)ans.push_back(tmp[i]+tmp[j]);
now++;
//if(ans.size()>p)break;
}
sort(ans.begin(),ans.end());
cout<<ans[p-1]<<endl;

		}
return 0;
}