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 <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 200000

// 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==-1)&&(P==-1)){
    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;
}

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

const int MAX=200000;
bool is_prime[MAX]={true};
vector<int> data;

void sieve(){
	is_prime[0]=is_prime[1]=false;
	for(int i=2;i*i<MAX;i++){
		if(is_prime[i]){
			for(int j=i*2;j<MAX;j+=i){
				is_prime[j]=false;
			}
		}
	}
}
int main(){
	fill(is_prime,is_prime+MAX,true);
	sieve();
	int n,p;
	while(cin>>n>>p &&n!=-1){
		data.clear();
		for(int i=n+1,c=0;c<300;i++){
			if(is_prime[i]){
				c++;
				for(int j=i,d=0;d<300;j++){
					if(is_prime[j]){
						d++;
						data.push_back(i+j);
					}
				}
			}
		}
		sort(data.begin(),data.end());
		cout<<data[p-1]<<endl;
	}

}

C++: #include <iostream>
#include <iomanip>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <climits>
#include <ctime>
#include <cassert>
using namespace std;

#define rep(i,a,n) for(int (i)=(a); (i)<(n); (i)++)
#define repq(i,a,n) for(int (i)=(a); (i)<=(n); (i)++)
#define repr(i,a,n) for(int (i)=(a); (i)>=(n); (i)--)
#define all(v) begin(v), end(v)
#define pb(a) push_back(a)
#define fr first
#define sc second
#define INF 2000000000
#define int long long int

#define X real()
#define Y imag()
#define EPS (1e-10)
#define EQ(a,b) (abs((a) - (b)) < EPS)
#define EQV(a,b) ( EQ((a).X, (b).X) && EQ((a).Y, (b).Y) )
#define LE(n, m) ((n) < (m) + EPS)
#define LEQ(n, m) ((n) <= (m) + EPS)
#define GE(n, m) ((n) + EPS > (m))
#define GEQ(n, m) ((n) + EPS >= (m))

typedef vector<int> VI;
typedef vector<VI> MAT;
typedef pair<int, int> pii;
typedef long long ll;

typedef complex<double> P;
typedef pair<P, P> L;
typedef pair<P, double> C;

int dy[]={0, 0, 1, -1};
int dx[]={1, -1, 0, 0};
int const MOD = 1000000007;

namespace std {
    bool operator<(const P& a, const P& b) {
        return a.X != b.X ? a.X < b.X : a.Y < b.Y;
    }
}

// [0,n) ???????????? i ???????????????primes[i] != 0 ??? i ????´???°
vector<int> erat(int n) {
    vector<int> primes(n);
    for (int i = 2; i < n; ++i) primes[i] = i;
    for (int i = 2; i*i < n; ++i)
        if (primes[i])
            for (int j = i*i; j < n; j+=i) primes[j] = 0;
    // ?´???°?????????vector???????´?????????´????????\?????????????????? (0 ??§??????????´??????¨??????)
    primes.erase(remove(primes.begin(), primes.end(), 0), primes.end());
    return primes;
}

signed main() {
    int n, p;
    vector<int> primes = erat(300000);
    while(cin >> n >> p) {
        if(n == -1 && p == -1) break;

        int st = upper_bound(primes.begin(), primes.end(), n) - primes.begin();

        vector<int> v;
        rep(i,st,st+20) {
            rep(j,i,st+20) {
                v.pb(primes[i] + primes[j]);
            }
        }
        sort(v.begin(), v.end());
        cout << v[p-1] << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#define pb push_back
#define all(v) v.begin(),v.end()
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
#define MAXBOOL 1000000
using namespace std;

int main(){
	int n,p;
	vector<int> prime;
	bool check[MAXBOOL];
	while(cin>>n>>p,n!=-1||p!=-1){
		prime.clear();
		fill(check,check+MAXBOOL,true);
		check[0]=check[1]=false;
		loop(i,2,sqrt(MAXBOOL)){
			for(int j=i*2;j<MAXBOOL;j+=i){
				check[j]=false;
			}
		}
		int cnt=0;
		while(prime.size()<=200){
			if(check[n+1+cnt])prime.pb(n+1+cnt);
			cnt++;
		}
		vector<int> ans;
		rep(i,prime.size()){
			loop(j,i,prime.size()){
				ans.pb(prime[i]+prime[j]);
			}
		}
		sort(all(ans));
		cout<<ans[p-1]<<endl;
	}
	return 0;
}