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++: // 2150.cpp
//
#include <bits/stdc++.h>
using namespace std;
const int MAX_N=110000;
const int MAX_P=100;

bool prime[MAX_N+1];
vector<int> t;
void sieve(){
  fill(prime,prime+MAX_N+1,1);
  prime[0]=prime[1]=0;
  for(int i=2;i<=MAX_N;++i){
    if(prime[i]){
      for(int j=i*2;j<=MAX_N;j+=i){
        prime[j]=0;
      }
      t.push_back(i);
    }
  }
}

int M(int n, int p){
  auto itr=upper_bound(t.begin(),t.end(),n);

  vector<int> sum;
  for(int i=0;i<p;++i)
    for(int j=i;j<p;++j)
      sum.push_back(*(itr+i) + *(itr+j));
  sort(sum.begin(),sum.end());
  return sum[p-1];
}
int main() {
  sieve();

  int n,p;
  while(cin>>n>>p){
    if(n==-1&&p==-1) break;
    cout<<M(n,p)<<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <algorithm>
#include <vector>
#include <utility>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <functional>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cassert>
 
using namespace std;
 
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define rep(i,n) REP(i, 0, n)
#define pb push_back
#define mp make_pair
#define all(r) (r).begin(),(r).end()
#define rall(r) (r).rbegin(),(r).rend()
#define fi first
#define se second
 
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;

const int INF = 1e9;
const double EPS = 1e-8;
const int mod = 1e9 + 7;
const ll LINF = 1e18;
const double PI = acos(-1);

struct Input
{
	int n;char c;char str[1024];string s;ll l;
	int nextInt(){scanf("%d", &n);return n;}
	ll nextLong(){scanf("%lld", &l);return l;}
	char nextChar(){scanf("%c", &c);return c;}
	string next(){scanf("%s", str);return string(str);}
	string nextLine(){getline(cin, s);return s;}
};
Input in;

bool isPrime[200000];
vector<int> primes;


int main(){
	rep(i, 200000) isPrime[i] = true;
	isPrime[0] = isPrime[1] = false;
	REP(i, 2, 200000){
		if(!isPrime[i]) continue;
		for(int j = i + i; j < 200000; j += i) isPrime[j] = false;
		primes.pb(i);
	}
	//cout<<primes.size()<<endl;
	while(1){
		int n = in.nextInt(),  p = in.nextInt();
		if(n == -1 && p == -1) break;
		
		vi v;
		int idx = upper_bound(all(primes), n) - primes.begin();
		for(int i = idx; i < primes.size(); i++){
			for(int j = idx; j < primes.size(); j++){
				if(v.size() < p + 1) v.pb(primes[i] + primes[j]);
				else{
					sort(all(v));
					if(v.back() > primes[i] + primes[j]){
						v.pop_back();
						v.pb(primes[i] + primes[j]);
					}
				}
			}
		}
		
		sort(all(v));
		printf("%d\n", v[p]);
	}
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string> 
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

int min_prime(int n);
int isprime(int n);

int main()
{
	int n, p;
	while(1){
		cin >> n >> p;
		if(n == -1 && p == -1) break;
		int prime_array[1000] = {0}, sum_array[1000];
		if(isprime(n)) prime_array[0] = n;
		else prime_array[0] = min_prime(n);
		for(int i = 0; i < 100; i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < p; i++){
			for(int j = i; j < p; j++){
				sum_array[k] = prime_array[i] + prime_array[j];
				k++;
			}
		}
		sort(sum_array, sum_array+k);
		cout << sum_array[p - 1] << endl;
	}
	return 0;
}

int min_prime(int n)
{
	int i = 1;
	while(1){
		if(isprime(n + i)) return n + i;
		else i++;
	}
}

int isprime(int n)
{
	int ans;
	if(n == 0 || n == 1) ans = 0;
	else if(n == 2) ans = 1;
	else {
		for(int i = 2; i < n; i++){
			if(i * i > n) ans = 1;
			else if(n % i == 0){
				ans = 0;
				break;
			}
		}
	}
	return ans;
}

C++: #include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

bool is_prime(int n, int k = 2)
{
    if(n < k * k) { return true; }
    
    if(n % k == 0) { return false; }
    
    return is_prime(n, k + 1);
}

int main()
{
    vector<int> prime;
    
    for(int i = 2; i < 150000; i++)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
    
    int n, m;
    
    while(true)
    {
        cin >> n >> m;
        
        if(n == 0 && m == 0) { break; }
        
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
        
        vector<int> c;
        
        for(int i = ptr; i < ptr + m; i++)
        {
            for(int j = i; j < ptr + m; j++)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
        
        sort(c.begin(), c.end());
        
        cout << c[m - 1] << endl;
    }
    
    return 0;
}