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 <bits/stdc++.h>
using namespace std;

#define FOR(i, a, n) for(int i = (a); i < (n); i++)
#define REP(i, n) for(int i = 0; i < (n); i++)
#define print(a) cout << a << "\n"
#define ALL(obj) (obj).begin(), (obj).end()
#define debug(x) cerr << #x << ": " << x << '\n'

#define MAX 250000



int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int prim[MAX];
  REP(i, MAX) {
    prim[i] = 1;
  }
  prim[0] = 0;
  prim[1] = 0;
  FOR(i, 2, sqrt(MAX)) {
    FOR(j, 2, MAX) {
      if(i * j > MAX) {
        break;
      }
      prim[i * j] = 0;
    }
  }

  vector<int> p;
  REP(i, MAX) {
    if(prim[i] == 1) {
      p.push_back(i);
    }
  }

  while(true){
    vector<int> sum;
    int N, P;
    cin >> N >> P;
    if(N + P == -2) break;

    REP(i, p.size()) {
      if(p[i] > N) {
        FOR(j, i, P + i) {
          sum.push_back(p[i] + p[j]);
        }
      }
    }

    sort(ALL(sum));

    cout << sum[P - 1] << endl;
  }

  return 0;
}

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

vector<int> ps;

void solve(int n, int p){
	auto ite = upper_bound(ps.begin(), ps.end(), n);
	vector<int> w;
	for(int i=0; i<p; ++i)
		for(int j=i; j<p; ++j)
			w.push_back(*(ite+i) + *(ite+j));
	sort(w.begin(), w.end());
//	for(int i=0; i<10; ++i)
//		cout << w[i] << "\n";
	cout << w[p-1] << "\n";
}

int main(){
//	cin.tie(0);
//	ios::sync_with_stdio(false);
	int cnt = 0;
	for(int i=2; cnt<101; ++i){
		bool f = true;
		for(int j=0; j<ps.size()&&ps[j]*ps[j]<=i; ++j)
			if(i % ps[j] == 0){
				f = false;
				break;
			}
		if(f){
			ps.push_back(i);
			if(i > 100000) ++cnt;
		}
	}
	while(1){
		int n, p;
		cin >> n >> p;
		if(n + p == -2) return 0;
		solve(n, p);
	}
}

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

#define NMAX 200274

void eratos(vector<bool> &hurui){
    int i = 1;
    hurui[0] = false;
    hurui[1] = false;
    while(true){
        i++;
        while(!hurui[i]){
            i++;
        }
        if(i*i > NMAX){
            break;
        }

        for(int j=i+i; j<=NMAX; j+=i){
            hurui[j] = false;
        }
    }
    return;
}

int main(){
    int n, p;
    vector<bool> hurui(NMAX+1, true);
    eratos(hurui);

    while(true){
        cin >> n >> p;
        if(n == -1){
            break;
        }
        
        vector<int> vec(p), ans;
        int pos = n+1;
        for(int i=0; i<p; i++){
            while(!hurui[pos]){
                pos++;
            }
            vec[i] = pos++;
        }
        
        for(int i=0; i<p; i++){
            for(int j=i; j<p; j++){
                ans.push_back(vec[i] + vec[j]);
            }
        }
        sort(ans.begin(), ans.end());

        cout << ans[p-1] << endl;;
    }
  
    return 0;
}

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

bool PN(int i){
	if(i == 2 || i == 3) return true;
	if(i <= 4 || i%2 == 0 || i%3 == 0) return false;
	for(int j = 6; (j-1)*(j-1) <= i; j+= 6) if((i%(j-1) == 0) || i%(j+1) == 0) return false;
	return true;
}

int main(){
	int N, P;
	while(1){
		int count = 0, PrimeNum[110] = {};
		vector <int> temp; 
		cin>>N>>P;
		if(N == -1 && P == -1) break;
		
		for(int i = N+1; count <= P; i++)
			if(PN(i)) PrimeNum[count++] = i;
		
		for(int i = 0; i <= P; i++)
			for(int j = i; j <= P; j++)
				temp.push_back(PrimeNum[i]+PrimeNum[j]);
		sort(temp.begin(), temp.end());
		cout<<temp[P-1]<<endl;
	}
		
	return 0;
}