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
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
#include <queue>

using namespace std;

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);

int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  const int MAXP = 110000;
  VI primes;
  vector<bool> isprime(MAXP, true);
  for(int i=2;i<MAXP;++i)
	if(isprime[i]){
	  primes.PB(i);
	  for(int j=i+i;j<MAXP;j+=i)
		isprime[j] = false;
	}

  while(true){
	int N, P; cin >> N >> P;
	if(N == -1) break;
	int idx = upper_bound(ALL(primes), N) - primes.begin();
	VI dm;
	REP(i,P) for(int j=i;j<P;++j)
	  dm.PB(primes[idx+i]+primes[idx+j]);
	SORT(dm);
	cout << dm[P-1] << endl;
  }
  
  return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <vector>
#include <list>
#include <cmath>
#include <fstream>
#include <algorithm>
#include <string>
#include <queue>
#include <set>
#include <map>
#include <complex>
#include <iterator>
#include <cstdlib>

using namespace std;

#define EPS (1e-10)
#define EQ(a,b) (abs((a) - (b)) < EPS)
#define EQV(a,b) (EQ((a).real(),(b).real()) && EQ((a).imag(),(b).imag()))

typedef complex<double> P;
typedef long long ll;

const int MAX_SIZE = 10000;
const int MAX_PRIME = 1000000;


int prime[MAX_PRIME+1];
bool isPrime[MAX_PRIME+1];
int p;

void erats(){
	// primeツδ環スツトツづーツ渉可甘コツ可サ
	fill(isPrime,isPrime+MAX_PRIME,true);
	p = 0;
	isPrime[0] = isPrime[1] = false;

	for(int i = 2; i <= MAX_PRIME; i++){
		if(isPrime[i]){
			prime[p++] = i;
		}
		else
			continue;
		// ツづ督づゥツつ「ツづ可つゥツつッツづゥ
		for(int j = 2*i; j <= MAX_PRIME; j+=i){
			isPrime[j] = false;
		}
	}
}

int main(){

	int N,P;
	erats();
	while(cin>>N>>P&&!(N==-1&&P==-1)){
		int *it = upper_bound(prime,prime+p,N);
		int prv=it-prime;
		int init=prv;
		vector<int> v;
		for(int i = init; i <= init+1000; i++){
			for(int j = i; j <= init+1000; j++){
				v.push_back(prime[i]+prime[j]);
			}
		}
		sort(v.begin(),v.end());
		cout<<v[P-1]<<endl;
	}

	return 0;
}

C++: // {{{ include and macros
#define debug(x) cout<<#x<<": "<<x<<endl
#define rep(i, a, b) for(int i=a; i < b;i++)
#include <algorithm>
#include <iostream>
#include <string>
#include <utility>
#include <vector>
#include <deque>
#include <set>
using namespace std;
// }}}

// {{{ io
void newline() {cout << endl;}
template <typename T>
void display(T input){cout << input;}
template <typename T>
void put(T input){display(input); newline();}
  // }}}

const int n_max = 100000;
const int prime_number_max = 200270;
const int p_max = 100;
vector<int> prime_numbers;
int n, p;

void reserve_prime_numbers(){
   const int sievesize = prime_number_max;
   std::vector<int> sieve(prime_number_max, 1);
   sieve.reserve(prime_number_max);
   for (int i = 2; i * i < sievesize; i++)
      if (sieve[i])
         for (int j = i + i; j < sievesize; j += i)
            sieve[j] = 0;
   for (int j = 2; j < sievesize; j++)
      if (sieve[j])
        prime_numbers.push_back(j);
}

int get_index(){
  int i=0;
  for(; prime_numbers[i]<=n; i++){}
  return i;
}

int binary_search_index_rec(int s, int e){
  int i=(s+e)/2;
  if(s==e-1){return i+1;}
  if(prime_numbers[i]==n){return i;}
  if(prime_numbers[i]>n) return binary_search_index_rec(s, e-(e-s)/2);
  if(prime_numbers[i]<n) return binary_search_index_rec(s+(e-s)/2, e);
}

int binary_search_index(){
  return binary_search_index_rec(0, prime_numbers.size()-1);
}

int solve(){
  vector<int> prime_numbers_sum;
  // int index = get_index();
  int index = binary_search_index();
  for(int i=0+index; i<25+index; i++){
    for(int l=i; l<25+index; l++){
      int sum = prime_numbers[i] + prime_numbers[l];
        prime_numbers_sum.push_back(sum);
    }
  }
  sort(prime_numbers_sum.begin(), prime_numbers_sum.end());
  return prime_numbers_sum[p-1];
}

int main(){
  ios::sync_with_stdio(false);
  prime_numbers.reserve(prime_number_max);
  reserve_prime_numbers();
  while(cin >> n >> p && n != -1 && p != -1)
    put(solve());
}