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<cmath>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<cstring>

using namespace std;

#define INF 999999999

bool pr[200000];

void erato(){
	pr[0] = false;
	pr[1] = false;
	pr[2] = true;
	for(int i=3;i<200000;i++){
		pr[i] = true;
		for(int j=2;j*j<=i;j++){
			if(i%j==0){
				pr[i] = false;
				continue;
			}
		}
	}
}

int main(){
	int i, j, n, p, now;
	erato();
	while(1){
		cin >> n >> p;
		if(n==-1) break;
		now = n*2+2;
		i=0;
		while(1){
			for(j=n+1;now-j>=j;j++){
				if(pr[j]&&pr[now-j]){
					//cout << j << " " << now-j << endl;
					i++;
				}
			}
			if(i>=p)break;
			now++;
		}
		cout << now << endl;
	}
	return 0;
}

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

const int MAX_N=1e6; // 1e8=x, 1e7=? 1e6=o
int n[MAX_N+1]={};

vector <int> prime;

void eratos_sieve(){
  for(int i=2;i<=MAX_N;i++){
    if(!n[i]){
      prime.push_back(i);
      for(int j=i;j<=MAX_N;j+=i) n[j]=1;
    }
  }
}

int main(){

  eratos_sieve();

  for(;;){
  int n,p;
  cin>>n>>p;
  if(!~n) break;

  vector <int> li,li_sum;
  auto origin=upper_bound(prime.begin(),prime.end(),n);
  int dis=distance(prime.begin(),origin);

  for(int i=dis;i<dis+p+1;i++) li.push_back(prime[i]);

  for(int i=0;i<(int)li.size();i++)
    for(int j=i;j<(int)li.size();j++)
      li_sum.push_back(li[i]+li[j]);

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

  cout<<li_sum[p-1]<<endl;

  }

  return 0;

}

C++: #include "bits/stdc++.h"

#define REP(i,n) for(ll i=0;i<n;++i)
#define RREP(i,n) for(ll i=n-1;i>=0;--i)
#define FOR(i,m,n) for(ll i=m;i<n;++i)
#define RFOR(i,m,n) for(ll i=n-1;i>=m;--i)
#define ALL(v) (v).begin(),(v).end()
#define PB(a) push_back(a)
#define UNIQUE(v) v.erase(unique(ALL(v),v.end()));
#define DUMP(v) REP(i, (v).size()) { cout << v[i]; if (i != v.size() - 1)cout << " "; else cout << endl; }
#define INF 1000000001ll
#define MOD 1000000007ll
#define EPS 1e-9

const int dx[8] = { 1,1,0,-1,-1,-1,0,1 };
const int dy[8] = { 0,1,1,1,0,-1,-1,-1 };


using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
///(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)///
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	vi prime = { 2 };
	FOR(i, 3,114514) {
		int flag = 1;
		REP(j, prime.size()) {
			if (i%prime[j] == 0)flag = 0;
		}
		if (flag)prime.push_back(i);
	}

	int n, p;
	while (1) {
		cin >> n >> p;
		if (n == -1)break;
		int c = lower_bound(ALL(prime), n) - prime.begin();
		vi v(p*p);
		REP(i, p) {
			REP(j, p) {
				v[i*p + j] = prime[i] + prime[j];
			}
		}
		sort(ALL(v));
		cout << v[p - 1] << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <iomanip>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <map>

#define MAX_N 100000
#define MAX_P 100

#define pb(s) push_back(s)
#define all(s) s.begin(), s.end()

using namespace std;

int N, P;
vector<int> prime;
vector<int> prime_sum;

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

void solve(){
	for (int i = N+1; i < N+1000; i++)
	{
		if(prime_judge(i)){
			prime.pb(i);
		}
	}
	for (int i = 0; i < prime.size(); i++)for(int j = i; j < prime.size(); j++) prime_sum.pb(prime[i]+prime[j]);
	sort(all(prime_sum));
	cout << prime_sum[P-1] << endl;
}

int main(){
	while(1){
		cin >> N >> P;
		if(N == -1) break;
		prime.clear();
		prime_sum.clear();
		solve();
	}
	return 0;
}