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 <vector>
#include <algorithm>
using namespace std;

vector<bool> prime(150000,true);

int main(){
    prime[0]=false;
    prime[1]=false;
    for(int i=2; i<150000; i++){
        if(prime[i]){
            for(int j=2; j*i<150000; j++){
                prime[j*i]=false;
            }
        }
    }

    while(1){
        int n,p;
        cin >> n >> p;
        if(n==-1) break;

        vector<int> prm(100);
        for(int i=n+1,cnt=0; cnt<p; i++){
            if(prime[i]){
                prm[cnt]=i;
                cnt++;
            }
        }

        vector<int> prmprd;
        for(int i=0; i<p; i++){
            for(int j=i; j<p; j++){
                prmprd.push_back(prm[i]+prm[j]);
            }
        }
        sort(prmprd.begin(),prmprd.end());
        cout << prmprd[p-1] << endl;



    }
    return 0;
}

C++: #include <map>
#include <set>
#include <list>
#include <cstdio>
#include <cmath>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cctype>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <iomanip>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional>

using namespace std;

#define fr first
#define sc second
#define mp make_pair

typedef long long int64;
typedef pair< int, int > iP;
typedef pair< iP, int > iiP;

const int INF = 2 << 28;
const double EPS = 1e-10;

#define MAX 200001

void makePrime(vector< bool > &isP, vector< vector< int > > &setP) {
    isP[0] = isP[1] = false;
    for(int i = 2; i * i < MAX; i++)
        for(int j = i + i; j < MAX; j += i)
            isP[j] = false;

    vector< int > tmp;
    for(int i = 2; i < MAX; i++)
        if(isP[i]) tmp.push_back(i);

    for(int i = 0; i < tmp.size(); i++) {
        for(int j = i; j < tmp.size(); j++) {
            setP[tmp[i] + tmp[j]].push_back(min(tmp[i], tmp[j]));
        }
    }


}

int main() {

    vector< vector< int > > setP(MAX * 2);
    vector< bool > isP(MAX, true);
    makePrime(isP, setP);

    int N, P;
    while(cin >> N >> P, ~N) {
        int cnt = 0;
        for(int i = 4; i < MAX * 2; i++) {
            for(int j = 0; j < setP[i].size(); j++) {
                if(setP[i][j] > N) cnt++;
                if(cnt == P) {
                    cout << i << endl;
                    break;
                }
            }
            if(cnt == P) break;
        }
    }
}

C++: #include <vector>
#include <iostream>
#include <utility>
#include <algorithm>
#include <string>
#include <deque>
#include <tuple>
#include <queue>
#include <functional>
#include <cmath>
#include <iomanip>
#include <map>
//cin.sync_with_stdio(false);
//streambuf
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
vector<char> pf(1000000, 1);
vector<int> prime;
int list[10000];
int main() {
	pf[0] = pf[1] = 0;
	for (int i = 2; i < 10000; i++) {
		if (!pf[i])continue;
		for (int j = 2 * i; j < 1000000; j += i)pf[j] = 0;
	}
	for (int i = 2; i < 1000000; i++) {
		if (pf[i])prime.push_back(i);
	}
	int n, p;
	while (cin >> n >> p, n!=-1) {
		auto ptr = lower_bound(prime.begin(), prime.end(),n+1);
		int cnt = 0;
		for (int i = 0; i < p; i++) {
			for (int j = i; j < p; j++) {
				list[cnt] = ptr[i] + ptr[j];
				cnt++;
			}
		}
		sort(list, list + cnt);
		cout << list[p - 1] << endl;
	}

}

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

int prime[300000];
void make_prime(){
  prime[0] = prime[1] = 1;
  for(int i = 2; i * i <= 300000; i++){
    if(!prime[i]){
      for(int j = i; i * j < 300000; j++){
        prime[i*j] = 1;
      }
    }
  }
}

int main(){
  int n, p;
  make_prime();
  while(cin >> n >> p){
    if(n == -1 && p == -1) break;
    int idx = n, cnt = 0;
    int sum[100] = {};
    while(cnt < 100){
      idx++;
      if(prime[idx] == 0){
        sum[cnt] = idx;
        cnt++;
      }
    }
    vector<int> ans;
    for(int i = 0; i < 100; i++){
      for(int j = i; j < 100; j++){
        ans.push_back(sum[i] + sum[j]);
      }
    }
    sort(ans.begin(), ans.end());
    cout << ans[p-1] << endl;
  }
  return 0;
}