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 <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() {
  while(1){
    cin>>N>>P;
    if(N==-1&&P==-1) break;
    vector<int> v;
    for(int i=N+1; ;i++){
      if(v.size()==1000) 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);
    }
    vector<int> nums;
    REP(i,0,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 <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define all(a) (a).begin(),(a).end()

typedef long long ll;
typedef pair<int, int> Pii;
typedef tuple<int, int, int> TUPLE;
typedef vector<int> V;
typedef vector<V> VV;
typedef vector<VV> VVV;

const int MAX_N = 300000;
vector<int> prime;
void setPrime(int n) {
    vector<bool> alive(n, true);
    alive[0] = alive[1] = false;
    rep2(i, 2, n + 1) {
        if (alive[i]) {
            prime.emplace_back(i);
            for (int j = 2 * i; j <= n; j += i) {
                alive[j] = false;
            }
        }
    }
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    setPrime(MAX_N);
    int n, p;
    while (cin >> n >> p, n != -1) {
        int s = upper_bound(all(prime), n) - prime.begin();
        vector<int> cand;
        rep(i, 100) {
            rep2(j, i, 100) {
                cand.emplace_back(prime[s + i] + prime[s + j]);
            }
        }
        sort(all(cand));
        cout << cand[p-1] << endl;
    }

}

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

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define ALL(a) (a).begin(),(a).end()
const int INF = INT_MAX/3;
const double EPS = 1e-14;

template<typename U, typename T>
void chmin(U &x, T y) { x = min(x, y); }

template<typename U, typename T>
void chmax(U &x, T y) { x = max(x, y); }

typedef long long int lli;

int N, P;

const int PRIMEMAX = 150000;
int FACTOR[PRIMEMAX];
vector<int> Primes;
void sieve(lli upb) {
  FACTOR[0] = FACTOR[1] = -1;
  for(lli n = 0; n < upb; ++n) {
    if (FACTOR[n] != 0) continue;
    Primes.push_back(n);
    lli kn = n * n;
    while (kn < PRIMEMAX) { FACTOR[kn] = n; kn += n; }
  }
}

bool is_prime(int n) {
  return FACTOR[n] == 0;
}

int main() {
  cout << fixed << setprecision(12);
  sieve(PRIMEMAX);
  while (cin >> N >> P and N != -1) {
    auto iter = upper_bound(ALL(Primes), N);
    vector<int> v;
    REP(i, 100) FOR(j, i, 100 + i) {
      v.push_back(*(iter + i) + *(iter + j));
    }
    sort(ALL(v));
    cout << v[P-1] << endl;
  }
  return 0;
}