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 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);
   prime_numbers.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;}
  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());
}

C++: #include <iostream>
#include <complex>
#include <sstream>
#include <string>
#include <algorithm>
#include <deque>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <vector>
#include <set>
#include <limits>
#include <cstdio>
#include <cctype>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
#define REP(i, j) for(int i = 0; i < (int)(j); ++i)
#define FOR(i, j, k) for(int i = (int)(j); i < (int)(k); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define REVERSE(v) reverse((v).begin(), (v).end())
typedef complex<double> P;
const int L = 1e7;
const int M = 30;

bool p[L];

void make_p(){
  REP(i, L) p[i] = true;
  p[0] = p[1] = false;
  for(int i = 2; i * i <= L; ++i){
    if(!p[i]) continue;
    for(int j = i + i; j < L; j += i) p[j] = false;
  }
}

int main() {
  make_p();
  int N, P;
  while(cin >>N >>P && N != -1){
    //vector<int> _p(M), v;
    //for(int i = N + 1, cnt = 0; cnt < M; ++i) if(p[i]) _p[cnt++] = i;
    //REP(i, M) FOR(j, i, M) v.push_back(_p[i] + _p[j]);
    //SORT(v);
    //cout <<v[P - 1] <<endl;
  }
  return 0;
}

C++: # include <iostream>
# include <algorithm>
# include <vector>
# include <string>
# include <set>
# include <map>
# include <cmath>
# include <iomanip>
# include <functional>
# include <utility>
# include <stack>
# include <queue>
# include <list>
# include <tuple>
# include <unordered_map>
# include <numeric>
# include <complex>
# include <bitset>
# include <random>
# include <chrono>
# include <cstdlib>
# include <tuple>
# include <array>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
constexpr int INF = 2147483647;
constexpr int HINF = INF / 2;
constexpr double DINF = 100000000000000000.0;
constexpr double HDINF = 50000000000000000.0;
constexpr long long LINF = 9223372036854775807;
constexpr long long HLINF = 4500000000000000000;
const double PI = acos(-1);
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
# define ALL(x)      (x).begin(),(x).end()
# define UNIQUE(c)   sort(ALL((c)));(c).erase(unique(ALL((c))),(c).end())
# define LOWER(s)    transform(ALL((s)),(s).begin(),TL<char>)
# define UPPER(s)    transform(ALL((s)),(s).begin(),TU<char>)
# define FOR(i,a,b)  for(LL i=(a);i<(b);i++)
# define RFOR(i,a,b) for(LL i=(a);i>=(b);i--)
# define REP(i,n)    FOR(i,0,n)
# define INIT        std::ios::sync_with_stdio(false);std::cin.tie(0)

std::vector<int> prime;
void MakePrime(int n) {
	prime.emplace_back(2);
	for (int i = 3; i <= n; i += 2) {
		bool a = false;
		for (int j = 3; j <= std::sqrt(i); j += 2) {
			if (i%j == 0) {
				a = true;
			}
		}
		if (a == false) {
			prime.emplace_back(i);
		}
	}
}

int n, p;

int main(){
	MakePrime(555555);
	while (cin >> n >> p&&(n!=-1)&&(p!=-1)) {
		int num = upper_bound(ALL(prime), n) - prime.begin();
		vector<int> ans;
		for (int i = num; i <= num + p + 1; i++) {
			for (int j = i; j <= num + p + 1; j++) {
				ans.emplace_back(prime[i] + prime[j]);
			}
		}
		sort(ALL(ans));
		cout << ans[p - 1] << endl;
	}
}