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 <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[50000] = {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 < (100 * p) + 1; i++){
            for(int j = i; j < (100 * 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 = 0;
    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;
                break;
            }
            else if(n % i == 0){
                ans = 0;
                break;
            }
        }
    }
    return ans;
}

C++: //41
#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

int main(){
  bool cmp[1000000]={true,true};
  vector<int> v;
  for(int i=2;i<1000000;i++){
    if(!cmp[i]){
      v.push_back(i);
      for(int j=2;i*j<1000000;j++){
	cmp[i*j]=true;
      }
    }
  }
  for(int n,p;cin>>n>>p,n!=-1;){
    vector<int> a;
    int x=upper_bound(v.begin(),v.end(),n)-v.begin();
    for(int i=0;i<100;i++){
      for(int j=i;j<i+100;j++){
	a.push_back(v[x+i]+v[x+j]);
      }
    }
    sort(a.begin(),a.end());
    cout<<a[p-1]<<endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<(int)(n);i++)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

constexpr int MAX_PR = 250000;

bool is_prime[MAX_PR];
vector<int> primes;

void solve(int N,int P){
    vector<int> v;
    int cnt = 0;
    for(int i=0;i<primes.size();i++){
        if(primes[i] <= N) continue;
        if(cnt++ == P*2) break;
        for(int j=i;j<primes.size();j++){
            if(primes[j] <= N) continue;
            v.push_back(primes[i]+primes[j]);
        }
    }
    sort(all(v));
    cout << v[P-1] << endl;
}


int main(){
    // prime
    rep(i,MAX_PR) is_prime[i] = true;
    is_prime[0] = is_prime[1] = false;
    for(int i=2;i<MAX_PR;i++){
        if(is_prime[i]){
            for(int j=2;i*j<MAX_PR;j++) is_prime[i*j] = false;
        }
    }
    for(int i=2;i<MAX_PR;i++) if(is_prime[i]) primes.push_back(i);

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