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

using namespace std;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
template<class T> inline T sqr(T x) {return x*x;}

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a)  (a).begin(),(a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#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 range(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)  range(i,0,n)
#define clr(a,b) memset((a), (b) ,sizeof(a))
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define v first
#define ind second

const double eps = 1e-10;
const double pi  = acos(-1.0);
const ll INF =1LL << 62;
const int inf =1 << 29;

int main(void){
	const int N = (int)1e6;
	vector<bool> isP(N, true);
    isP[0] = isP[1] = false;
	for(int i = 2; i * i < N; i++) if(isP[i]) for(int j = i; i * j < N; j++) isP[i * j] = false;

    vi P;
    rep(i, N){
        if(isP[i]) P.pb(i);
    }

    for(int n, p, res; cin >> n >> p, n != -1; cout << res << endl){
        vector<pii> s(100);
        int pos = upper_bound(all(P), n) - P.begin();

        rep(i, s.size()){
            s[i].first = 2 * P[pos + i];
            s[i].second = pos + i;
        }

        rep(i, p){
            vector<pii>::iterator itr = min_element(all(s));
            res = itr->v;
            
            itr->v += P[itr->ind + 1] - P[itr->ind++];
        }
    }

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#define REP(i, a, n) for(int i = ((int) a); i < ((int) n); i++)
using namespace std;

int N, P;
bool p[300000];
vector<int> prime;

int main(void) {
  REP(i, 0, 300000) p[i] = 1;
  p[0] = p[1] = 0;
  REP(i, 2, 300000) if(p[i]) for(int j = i * 2; j < 300000; j += i) p[j] = 0;
  REP(i, 0, 300000) if(p[i]) prime.push_back(i);

  while(cin >> N >> P, N != -1) {
    int m;
    REP(i, 0, prime.size()) if(prime[i] > N) {
      m = i;
      break;
    }

    vector<int> v;
    REP(i, m, m + P) REP(j, i, m + P) v.push_back(prime[i] + prime[j]);
    sort(v.begin(), v.end());
    cout << v[P - 1] << endl;
  }

  return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vint;
typedef pair<int, int> pii;

#define abs(a) ((a) < (0)? -(a):(a))
#define rep(i, n) REP(i, 0, (n))
#define REP(i, a, n) for(int i=(a); i<(n); i++)
#define pb push_back

int N = 110000;
bool is_prime[110000];

void set_prime() {
    rep(i, N) is_prime[i] = true;
    is_prime[0] = is_prime[1] = false;
    REP(i, 2, sqrt(N)) {
        if(is_prime[i]) {
            for(int j=0; i*(j+2)<N; j++) {
                is_prime[i*(j+2)] = false;
            }
        }
    }
}

int main() {
    set_prime();
    int n, p;
    while(cin>>n>>p, n+p>0) {
        vint v;
        for(int i=n, j = 0; j<20; i++) {
            if(is_prime[i]) j++, v.pb(i);
        }
        vint w;
        rep(i, v.size()) REP(j, i, v.size()) {
            w.pb(v[i]+v[j]);
        }
        sort(w.begin(), w.end());
        
        //cout << n << ", "<< p <<  ", "<<  w.size()  <<  ", "<<  v.size() << endl;
        cout <<  w[p-1] << endl;
    }
}

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

const int LIM = 3000000;

char isprime[LIM];
int primes[LIM];
int PRIME_LIM = 0;

void eratosthenes() {
    fill(isprime, isprime + LIM, 1);
    isprime[0] = isprime[1] = 0;

    for(int x = 2; x * x < LIM; ++x) {
        if(!isprime[x]) continue;

        for(int y = x * x; y < LIM; y += x) {
            isprime[y] = 0;
        }
    }

    for(int x = 0; x < LIM; ++x) {
        if(isprime[x]) {
            primes[PRIME_LIM++] = x;
        }
    }
}

int solve(int N, int P) {
    vector<int> mtseq;
    int* ub = upper_bound(primes, primes + PRIME_LIM, N);

    for(int s = 0; s <= P; ++s) {
        for(int j = 0; j <= s; ++j) {
            int m = ub[s] + ub[j] - 2 * N;
            mtseq.push_back(m);
        }
    }

    sort(begin(mtseq), end(mtseq));

    return mtseq[P - 1];
}

int main() {
    eratosthenes();
    int N, P;
    while(true) {
        cin >> N >> P;
        if(N == -1 && P == -1) break;
        cout << solve(N, P) << endl;
    }
    return 0;
}