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>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<string> vs;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<ll,pll> pip;
typedef vector<pip> vip;
const int inf=1<<30;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-11;
const ll mod=1e9+7;
const int dx[4]={-1,0,1,0},dy[4]={0,-1,0,1};

const int NPrime=1000000;
bool prime[NPrime+1];
vi EnumeratePrime(){
	fill(prime+2,prime+NPrime+1,true);
	vi a;
	for(int i=2;i<=NPrime;i++) if(prime[i]){
		a.emplace_back(i);
		for(int j=2*i;j<=NPrime;j+=i) prime[j]=0;
	}
	return a;
}

int n,m;

int main(){
	EnumeratePrime();
	while(1){
		cin>>n>>m;
		if(n==-1) break;
		vi b;
		for(int i=n+1;b.size()<m;i++){
			if(prime[i]) b.push_back(i);
		}
		vi c;
		for(int i=0;i<m;i++) for(int j=i;j<m;j++) c.push_back(b[i]+b[j]);
		sort(c.begin(),c.end());
		cout<<c[m-1]<<endl;
	}
}

C++: #include <bits/stdc++.h>

using namespace std;

const int MAX=1299709;
int prime[MAX+1]={0};//0::prime 1::NOTprime;

void hurui(){
  prime[1]=1;
  for(int i=1;i*i<=MAX;i++){
    for(int j=2;j<=MAX/i;j++){
      if(prime[i]==0)prime[i*j]=1;
    }
  }
}

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

  std::vector<int> v;
  for(int i=1;i<=MAX;i++) if(prime[i]==0)v.push_back(i);
  int n,p;
  while(true){
    cin >> n >> p;
    if(n==-1) break;
    std::vector<int> li;
    int idx=0;
    while(v[idx]<=n)idx++;
    for(int i=idx;i<idx+p;i++){
      for(int j=i;j<idx+p;j++){
          li.push_back(v[i]+v[j]);
      }
    }
    sort(li.begin(),li.end());
    cout<<li[p-1]<<endl;
  }
}

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
  int a[10000]={2,3},i,j,k,c=2,b[120000][170],q;
  for(i=4;i<100000;i++){
    for(k=1,j=2;j*j<=i;j++){
      if(i%j==0){k=0;break;}
    }
    if(k)a[c++]=i;
  }k=0;
  for(i=0;i<120000;i++){
    if(i>a[k])k++;
    for(q=0,j=k;j<k+13;j++){
      for(c=k;c<k+13;c++){
        b[i][q++]=a[j]+a[c];
      }
    }
    sort(b[i],b[i]+169);
  }
  while(cin>>i>>j,i||j)cout<<b[i][j]<<endl;
}