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 <algorithm>
#include <string>
#include <vector>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <utility>
#include <ctime>
#define INF 999999999
#define mod 1000000007

#define rep(i,n) for(int i=0;i<int(n);i++)
#define rrep(i,n) for(int i=(n);i>=0;i--)
#define REP(i,a,b) for(int i=(a);i<int(b);i++)
#define all(x) (x).begin(),x.end()
#define pb push_back
#define mp make_pair
#define MOD(x) (x%(mod))
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef pair<int,int> pi;

int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
bool debug=false;
/*---------------------------------------------------*/

int prime[15000];
bool is_prime[150000];

void prime_judge(){
  int p=0;
  rep(i,150000)is_prime[i]=true;
  is_prime[0]=is_prime[1]=false;
  for(int i=2;i<150000;i++){
    if(is_prime[i]){
      prime[p++]=i;
      for(int j=i*2;j<=150000-1;j+=i)is_prime[j]=false;
    }
  }
}


int binary_search(int n){
  int l=0,r=13848;
  int i;
  while(r-l>=1){
    i=(l+r)/2;
    if(prime[i]==n)return i+1;
    else if(prime[i]<n) l=i+1;
    else r=i;
  }
  if(prime[i]<n)i++;
  return i;
}

void matuzaki(int n,int p){
  vi v;
  int near=binary_search(n);
  for(int i=near;i<=near+21;i++){
    for(int j=i;j<=near+21;j++){
      v.pb(prime[i]+prime[j]);
    }
  }
  sort(all(v));
  printf("%d\n",v[p-1]);
}

int main(){
  int n,p;
  prime_judge();
  while(1){
    scanf("%d%d",&n,&p);
    if(n==-1&&p==-1)break;
    matuzaki(n,p);
  }
  return 0;
}

C++: #include<iostream>
#include<string>
using namespace std;
long long m[100],c[10000];
int main(){
	long long n,p;
	while(true){
		cin>>n>>p;
		if(n==-1&&p==-1)
			break;
		for(int i=0;i<p*p;i++){
			c[i]=1000000;
		}
		if(n==0)
			n++;
		int i=n+1,count=0;
		while(true){
			bool t=true;
			for(int j=2;j*j<=i;j++){
				if(i%j==0)
					t=false;
			}
			if(t==true){
				m[count]=i;
				count++;
			}
			if(count==p)
				break;
			i++;
		}
		for(int i=0;i<p;i++){
			for(int j=0;j<=i;j++){
				c[i*p+j]=m[i]+m[j];
			}
		}
		for(int i=0;i<p*p-1;i++){
			for(int j=p*p-1;j>i;j--){
				if(c[j]<c[j-1]){
					int tmp=c[j];
					c[j]=c[j-1];
					c[j-1]=tmp;
				}
			}
		}
		cout<<c[p-1]<<endl;
	}
	return 0;
}

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

using namespace std;

bool is_prime[1 << 22];
vector<int> prime;

void sieve(int n) {
  fill(is_prime, is_prime + n, true);
  for (int i = 2; i <= n; i++) {
    if (!is_prime[i]) continue;
    prime.push_back(i);
    for (int j = 2 * i; j <= n; j += i) {
      is_prime[j] = false;
    }
  }
}

int main(void) {
  sieve(210000);

  int n, p;
  while (cin >> n >> p, n >= 0) {
    int l = 0;
    while (prime[l] <= n) l++;

    vector<int> sub, sum;
    for (int i = 0; i < 30; i++) {
      sub.push_back(prime[l + i]);
    }
    for (int i = 0; i < 30; i++) {
      for (int j = i; j < 30; j++) {
        sum.push_back(sub[i] + sub[j]);
      }
    }
    sort(sum.begin(), sum.end());

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

  return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define o(a) cout << a << endl
#define int long long
#define fi first
#define se second
using namespace std;
typedef pair<int, int> P;

const int MAX_N = 200010;
int prime[MAX_N];
bool is_prime[MAX_N + 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;
        }
    }
}


signed main(){
    int n, p;
    sieve(200000);
    while(1){
        cin >> n >> p;
        if(n == -1 && p == -1) break;
        int ans = 0;
        vector<int> d;
        set<int> st;
        int id = -1;
        rep(i, 0, 200010){
            if(prime[i] > n){
                id = i;
                break;
            }
        }
        rep(i, 0, 200){
            rep(j, i, 200){
                int sum = prime[id + i] + prime[id + j];
                // if(!st.count(sum)){
                    d.push_back(sum);
                    st.insert(sum);
                // }
            }
        }
        sort(all(d));
        cout << d[p - 1] << endl;
    }
}