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 <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
#include <cstring>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
#define CLR(mat) memset(mat, 0, sizeof(mat))
typedef long long ll;
const ll MAX = 150000;
bool isPrime[MAX];
vector<ll> prime;
void makePrime(){
  for (ll i = 0; i < MAX; i++){
    isPrime[i] = true;
  }
  for (ll i = 2; i * i < MAX + 1; i++){
    if(isPrime[i]){
      for (ll j = 2 * i; j < MAX; j += i) {
        isPrime[j] = false;
      }
    }
  }
  FOR(i,2,MAX) if(isPrime[i]) prime.push_back(i);
  return;
}
int main()
{
  makePrime();
  int N, R;
  while(cin >> N >> R, N != -1) {
    int j = upper_bound(prime.begin(), prime.end(), N) - prime.begin();
    vector<int> v;
    FOR(i,j,j+200) {
      FOR(k,i,j+200) {
        v.push_back(prime[i]+prime[k]);
      }
    }
    sort(v.begin(), v.end());
    cout << v[R-1] << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using lint = long long int;
using ulint = unsigned long long int;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;
template<class T, class U> void assign(V<T>& v, int n, const U& a) { v.assign(n, a); }
template<class T, class... Args> void assign(V<T>& v, int n, const Args&... args) { v.resize(n); for (auto&& e : v) assign(e, args...); }


template<class Int> V<Int> sieve(Int a, Int b) {
  a = max<Int>(2, a); V<Int> res; Int q = ceil(sqrt(b));
  V<bool> mem(b - a, true), sub(q - 2, true);
  for (Int i = 2; i < q; ++i) {
    if (sub[i - 2]) {
      for (Int j = max(i, (a + i - 1) / i) * i; j < b; j += i) mem[j - a] = false;
      for (Int j = i * i; j < q; j += i) sub[j - 2] = false;
    }
  }
  for (Int i = a; i < b; ++i) if (mem[i - a]) res.push_back(i);
  return res;
}

int main() {
  cin.tie(nullptr); ios_base::sync_with_stdio(false);
  while (true) {
    int n, p; cin >> n >> p, --p;
    if (n == -1) break;
    auto ps = sieve<int>(n + 1, 1e6);
    assert(ps.size() > p);
    V<> v;
    for (int i = 0; i <= p; ++i) for (int j = 0; j <= i; ++j) {
      v.push_back(ps[i] + ps[j]);
    }
    sort(begin(v), end(v));
    cout << v[p] << '\n';
  }
}

C++: #include <vector>
#include <iostream>
#include <algorithm>
 
using namespace std;
 
bool is_prime(int n, int k = 3)
{
    if(n < k * k) { return true; }
     
    if(n % k == 0) { return false; }
     
    return is_prime(n, k + 2);
}
 
int main()
{
    vector<int> prime = {2};
     
    for(int i = 3; i < 101300; i += 2)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
     
    int n, m;
     
    while(true)
    {
        scanf("%d", &n);
        scanf("%d", &m);
         
        if(n == -1 && m == -1) { break; }
         
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
         
        vector<int> c; int r = min(30, m) - 1;
        
        for(int i = ptr + r; i >= ptr; i--)
        {
            for(int j = ptr + r; j >= i; j--)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
        
        sort(c.begin(), c.end());
         
        printf("%d\n", c[m - 1]);
    }
     
    return 0;
}

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

const int MAX_=1000000;

bool is_prime[MAX_];
vector<int> prime;

bool sieve(){
	fill(is_prime,is_prime+MAX_,true);
	is_prime[0]=is_prime[1]=false;
	for(int i=2; i<MAX_; ++i){
		if(is_prime[i]){
			prime.push_back(i);
			for(int j=2*i; j<MAX_; j+=i){
				is_prime[j]=false;
			}
		}
	}
}

int solve(int n,int p){
	vector<int> sum_prime;
	auto it=upper_bound(prime.begin(),prime.end(),n);
	//cout << *it << endl;
	for(int i=0; it!=prime.end()&&i<p; ++it,++i){
		auto it_=it;
		for(int j=0; it_!=prime.end()&&j<p; ++it_,++j){
			sum_prime.push_back((*it)+(*it_));
			//cout << (*it)+(*it_) << endl;
		}
	}
	sort(sum_prime.begin(),sum_prime.end());
	return sum_prime[p-1];
}

int main(){
	int N,P;
	sieve();
	while(cin>>N>>P&&!(N==-1&&P==-1)){
		cout << solve(N,P) << endl;
	}
	return 0;
}