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 <vector>
#include <iostream>
#include <algorithm>
 
using namespace std;
 
bool is_prime(int n, int k = 3)
{
    if(n < k * k) { return true; }
     
    if(n % k == 0) { return false; }
     
    return is_prime(n, k + 2);
}
 
int main()
{
    vector<int> prime = {2};
     
    for(int i = 3; i < 101300; i += 2)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
     
    int n, m;
     
    while(true)
    {
        scanf("%d", &n);
        scanf("%d", &m);
         
        if(n == -1 && m == -1) { break; }
         
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
         
        vector<int> c;
         
        for(int i = ptr; i < ptr + m; i++)
        {
            for(int j = i; j < ptr + m; j++)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
         
        sort(c.begin(), c.end());
         
        printf("%d\n", c[m - 1]);
    }
     
    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>

#define CH(N,A,B) (A<=N&&N<B)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define RREP(i,a,b) for(int i=(b-1);a<=i;i--)

using namespace std;

int N, P;

int main() {
  vector<int> v;
  for(int i=2; ;i++){
    if(v.size()==10000) break;
    if(i<2) continue;
    bool flag = true;
    for(int j=2; j*j<=i; j++){
      if(i%j == 0){
        flag = false;
        break;
      }
    }
    if(flag) v.push_back(i);
  }

  while(1){
    cin>>N>>P;
    if(N==-1&&P==-1) break;
    int pos;
    REP(i,0,v.size()){
      if(N<v[i]){
        pos = i;
        break;
      }
    }
    vector<int> nums;
    REP(i,pos,v.size()){
      REP(j,i,v.size()){
        int num = v[i]+v[j];
        nums.push_back(num);
      }
    }
    sort(nums.begin(),nums.end());
    cout<<nums[P-1]<<endl;
  }

  return 0;
}

C++: #include <iostream>
#include <bitset>
#include <vector>
#include <algorithm>

using namespace std;

const int MAX_N = 2000000;

bitset<MAX_N> sieve;
vector<int> primes;
void eratosthenes(){
	sieve[0] = sieve[1] = true;
	for(int i = 2; i < MAX_N; ++i){
		if(sieve[i]){ continue; }
		primes.push_back(i);
		for(int j = i + i; j < MAX_N; j += i){ sieve[j] = true; }
	}
}

int main(){
	eratosthenes();
	while(true){
		int n, p;
		cin >> n >> p;
		if(n == 0 && p == 0){ break; }
		int begin =
			upper_bound(primes.begin(), primes.end(), n) - primes.begin();
		vector<int> pp;
		for(int i = 0; i < 200; ++i){
			for(int j = 0; j <= i; ++j){
				pp.push_back(primes[begin + i] + primes[begin + j]);
			}
		}
		sort(pp.begin(), pp.end());
		cout << pp[p - 1] << endl;
	}
	return 0;
}

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

bool e[150010];

void erato(){
	fill(e, e+150010, true);
	e[0] = e[1] = false;

	for(int i=0; i < 150010; i++){
		if(!e[i]) continue;
		for(int j=i+i; j < 150010; j += i){
			e[j] = false;
		}
	}
}

int main(){
	erato();

	int n, p;
	int primeNumbers[100];
	int addPrimeNumbers[100010];
	while(cin >> n >> p, n != -1 && p != -1){
		while(1){
			if(e[++n]) break;
		}
		for(int i=0; i < p; n++){
			if(e[n]){
				primeNumbers[i] = n;
				i++;
			}
		}
		int countPrimeNumbers = 0;
		for(int i=0; i < p; i++){
			for(int j=i; j < p; j++){
				addPrimeNumbers[countPrimeNumbers] =  primeNumbers[i] + primeNumbers[j];
				countPrimeNumbers++;
			}
		}
		sort(addPrimeNumbers, addPrimeNumbers + countPrimeNumbers);

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

C++: #include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
using namespace std;

#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<pii, int> ppi;

#define INF 1000000000
#define MAX 2000000

// sieve of Eratosthenes (prime num)
bool p[MAX+1]; //prime number=true
void prime(int n){
  rep(i,n+1) p[i]=true;
  p[0]=p[1]=false;
  for(int i=2;i<=n;i++){
    if(p[i]){
      for(int j=i*2; j<=n; j+=i){
	p[j]=false;
      }
    }
  }
}


int main(){
  prime(MAX);
  int n,P;
  while(scanf("%d %d", &n, &P), n^P){
    int nums[100];
    vector<int> adds;

    // take P prime number bigger than n
    int cnt=0, idx=n+1;
    while(cnt<P){
      if(p[idx]){
	nums[cnt]=idx;
	cnt++;
	rep(i,cnt){
	  adds.pb(nums[i]+idx);
	}
      }
      idx++;
    }

    sort(all(adds));

    cout << adds[P-1] << endl;

  }
  return 0;
}