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 <cstdlib>
#include <algorithm>

using namespace std;
const static int N_MAX = 1000000;
const static int P_MAX = 101;

int era[ N_MAX ] = { 0 };
int primeList[ N_MAX ];
int invPrimeList[ N_MAX ];
int ctr = 0;

int main() {
  era[ 0 ] = 1;
  era[ 1 ] = 1;
  for( int i = 2; i < N_MAX; i++ ) {
    if( era[ i ] ) { continue; }
    for( int j = i * 2; j < N_MAX; j += i ) {
      era[ j ] = 1;
    }
  }
  
  for( int i = 0; i < N_MAX; i++ ) {
    if( !era[ i ] ) {
      invPrimeList[ i ] = ctr;
      primeList[ ctr++ ] = i;
    }
  }

  while( 1 ) {
    int n, p;
    int table[ P_MAX * P_MAX ];
    cin >> n >> p;
    if( n == -1 && p == -1 ) { return EXIT_SUCCESS; }

    int i;
    for( i = n + 1; i < N_MAX; i++ ) {
      if( !era[ i ] ) { break; }
    }

    int pid = invPrimeList[ i ];
    int k = 0;
    for( int i = 0; i < P_MAX; i++ ) {
      for( int j = i; j < P_MAX; j++ ) {
        table[ k++ ] = primeList[ pid + i ] + primeList[ pid + j ];
      }
    }

    sort( table, table + k );
    
    cout << table[ p - 1 ] << endl;
  }
}

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

using namespace std;

void eratosthenes(vector<int> &n){	
	n[0] = n[1] = 1;
	for (int i = 2;i <= 120000; i++){
		if (n[i] == 0){
			for (int j = 2; j <= (120000/i); j++){
				n[i * j] = 1;
			}

		}
	}
	return;
}

bool isPrime(int n){
	if (n < 2) return false;
	if (n == 2) return true;
	for (int i = 2; i <= sqrt(n) + 1; i++){
		if (n % i == 0) return false;
	}
	return true;
}
		
int main(){
	vector<int> era(120000);
	eratosthenes(era);
	vector<int> Primelist(120001);
	int index = 1;
	for (int i = 1; i <= era.size(); i++){
		if (era[i] == 0){
			Primelist[index] = i;
			index++;
		}
	}
	while(1){
		int n,p; cin >> n >> p;
		if (n + p == -2) break;
		index = 1;
		while(n >= Primelist[index]){
			index++;
		}
		
		vector<int> list(120000);
		for (int i = 1; i <= p; i++){
			for (int j = i; j <= p; j++){
				list[(i-1) * p + j] = Primelist[index + i - 1] + Primelist[index + j - 1];
			}
		}
		sort(list.begin(),list.end());
		index = 0;
		while(list[index] == 0){
			index++;
		}
		cout << list[index + p - 1] << endl;
		
	}

return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
#define N 1000000
using namespace std;
int main(){
  vector<int> m,mn;
  int n[N]={},s,t,st;
  n[0]=1,n[1]=1;
  for(int i=2;i<=1000;i++)
    for(int j=2;i*j<N;j++)if(n[j*i]==0) n[i*j]=1;
  for(int i=0;i<N;i++) if(n[i]==0) m.push_back(i);
  while(1){
    cin>>s>>t;
    if(s+t==-2) break;
    for(int i=0;i<m.size();i++) if(m[i]>s){
	st=i;
	break;
      }
    for(int i=st;i<t+st;i++)
      for(int j=i;j<t+st;j++) mn.push_back(m[i]+m[j]);
    sort(mn.begin(),mn.end());
    cout<<mn[t-1]<<endl;
    mn.clear();
  }    
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define all(x) (x).begin(),(x).end()
const int mod=1000000007,MAX=200005,INF=1<<30;

int prime[MAX];//i番目の素数
bool is_prime[MAX+1];

void sieve(int n){
    int p=0;
    for(int i=0;i<=n;i++){
        is_prime[i]=true;
    }
    
    is_prime[0]=is_prime[1]=false;
    
    for(int i=2;i<=n;i++){
        if(is_prime[i]){
            prime[p++] = i;
            for(int j=2*i;j<=n;j+=i){
                is_prime[j] = false;
            }
        }
    }
}

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    sieve(MAX-3);
    
    while(1){
        int N,P;cin>>N>>P;
        if(N==-1&&P==-1) break;
        vector<int> A;
        
        for(int i=N+1;;i++){
            if(is_prime[i]){
                A.push_back(i);
            }
            if(A.size()==P) break;
        }
        
        multiset<int> SE;
        for(int i=0;i<P;i++){
            for(int j=i;j<P;j++){
                SE.insert(A[i]+A[j]);
            }
        }
        
        for(auto it=SE.begin();P;it++){
            if(P==1) cout<<*it<<endl;
            P--;
        }
    }
    
}

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;
}