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 REP(i, n) for (int i = 0; i < n; i++)
#define ALL(obj) obj.begin(), obj.end()
#define fcout cout << setprecision(10)

const int iINF = 1e9;
const long long llINF = 1e18;
const int MOD = 1e9 + 7;

using namespace std;

template <typename T>
void debug(vector<T> &vec) {
    for (auto x : vec) {
        cout << x << " ";
    }
    cout << endl;
    return;
}

template<typename A, size_t N, typename T>
void FILL(A (&array)[N], const T &val){
    std::fill( (T*)array, (T*)(array+N), val );
}

template <typename T>
int getFormer(const vector<T> &vec, T x) {
    return upper_bound(vec.begin(), vec.end(), x) - vec.begin() - 1;
}

template <typename T>
int getLatter(const vector<T> &vec, T x) {
    return lower_bound(vec.begin(), vec.end(), x) - vec.begin();
}

vector<long long> era(int N) {
    vector<bool> isPrime(N, true);
    vector<long long> res;
    isPrime[0] = isPrime[1] = false;
    for (int i = 2; i < sqrt(N) + 1; i++) {
        if (isPrime[i] == true) {
            res.push_back(i);
            for (int j = i + i; j < N + 1; j += i){
                isPrime[j] = false;
            }
        }
    }

    return res;
}

vector<long long> primes;

int solve(int N, int P) {
    auto s = lower_bound(ALL(primes), N) - primes.begin();
    vector<long long> sums;
    for (int i = s; i < s + P; i++) {
        for (int j = i; j < s + P; j++) {
            sums.push_back(primes[i] + primes[j]);
        }
    }

    sort(ALL(sums));
    debug(sums);
    cout << sums[P - 1] << endl;
}

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

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

using namespace std;

#define MAX 1000001

vector<int> vprimes;
bool *isPrime = new bool[MAX];

/* ツ素ツ青板青カツ青ャ O(n^2) */
void MakePrime(){
  isPrime[0]=false;
  isPrime[1]=false;
  isPrime[2]=true;
  for(int i = 2; i < MAX; ++i){
    isPrime[i] = true;
  }
  for(long long int i = 2; i < MAX; ++i){
    if( isPrime[i] ){
      for(long long int j = 2; i * j < MAX; ++j) {
	isPrime[i*j] = false;
      }
    }
  }
  for(int i = 0; i < MAX; ++i){
    if( isPrime[i] ){
      vprimes.push_back( i );
    }
  }
}

int main()
{
  MakePrime();
  int N,P;
  while(cin>>N>>P&&(N>=0)&&(P>=0)){
    vector<int> v;
    vector<int> primes;
    for(int i = 0; i < vprimes.size(); ++i){
      if(vprimes[i]>N){
	primes.push_back(vprimes[i]);
      }
    }
    for(int i = 0; i < primes.size(); ++i){
      for(int j = i; j < P; ++j){
	v.push_back(primes[i]+primes[j]);
      }
    }
  end:;
    nth_element(v.begin(),v.begin()+P,v.end());
    cout << v[P-1] << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <algorithm>
using namespace std;
bool prime[300005];

void init(void){
  for(int i = 0 ; i < 300005 ; i++){prime[i] = true;}
  prime[0] = false, prime[1] = false;
  for(int i = 2 ; i < 300005 ; i++){
    if(prime[i] == true){
      for(int k = 2 ; i * k < 300005 ; k++){
	prime[i * k] = false;
      }
    }
  }
}

int main(void){
    init();
    for(;;){
        int N, P;
        cin >> N >> P;
	if(N == -1 && P == -1){return 0;}
        int p[100];
        int ptr=0;
        for(int i = N + 1 ; ptr<100 ; i++){
            if(prime[i]){p[ptr] = i; ptr++;}
        }
        int sum[50*101]; ptr=0;
        for(int i = 0 ; i < 100 ; i++){
            for(int j = i ; j < 100 ; j++){
                sum[ptr] = p[i] + p[j]; ptr++;
            }
        }
	sort(sum, sum+5050);
        cout << sum[P-1] << endl;
    }
}

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cmath>
#include<utility>
#include<set>
#include<complex>
#define vi vector<int>
#define vvi vector<vector<int> >
#define ll long long int
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vb vector<bool>
#define vc vector<char>
#define vs vector<string>
#define ld long double
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define CC puts("-------ok--------");
#define all(in) in.begin(), in.end()
#define bv vector<bool>
using namespace std;
typedef pair<int, int> PI;
#define MAX 1e7
int main(){
    int n,n2;
    vector<bool>check(MAX+1,true);
    vector<int>Primenumber(MAX+1,0); //Primearray
    int counter =0;                  //Primearray counter;
    for(int i = 2; i<MAX+1;i++){
        if(check[i]){
            for(int j = 2;i*j<MAX;j++)
                check[i*j] = false;//?´???°??????Primearray???????´??????????????????°?????¨???false???
            Primenumber[counter] = i;
            counter++;
        }
    }
    check[0]=false;
    check[1]=false;
    while(cin>>n>>n2,n+n2+2){
        vi v; int count=0;
        for(int i=2*n;;i++){
            if(i<4)continue;
            //cout<<i<<endl;
            for(int j=i;(double)j>=(double)i/2;j--){
                if(check[j]&&check[i-j]&&i-j>n&&j>n){v.push_back(i);count++;}
                if(count>n2)goto E;
            }
        }
    E:cout<<v[n2-1]<<endl;
    }
}