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<string>
#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cmath>
#include<utility>
#include<set>
#include<complex>
#include<map>
#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 loop(i,s,n) for(int i=s;i<n;i++)
#define all(in) in.begin(), in.end()
#define MAX 9e5
using namespace std;
typedef pair<int, int> pii;
int main(){
    vector<bool>Primecheck(MAX+1,true);
    vector<int>Primenumber(MAX+1,0); //Primearray
    int Primecounter =0;                  //Primearray counter;
    for(int i = 2; i<MAX+1;i++){
        if(Primecheck[i]){
            for(int j = 2;i*j<MAX;j++)
                Primecheck[i*j] = false;//?´???°??????Primearray???????´??????????????????°?????¨???false???
            Primenumber[Primecounter] = i;
            Primecounter++;
        }
    }
    int n,m;
    while(cin>>n>>m,n+m>=0){
        int cnt=0;
        for(int i=0; i<Primenumber.size();i++){
            if(Primenumber[i]>n){cnt=i;break;}
        }
        vi v;
        for(int i=cnt; i<=cnt+m;i++){
            for(int j=i; j<=cnt+m;j++){
                v.push_back(Primenumber[i]+Primenumber[j]);
            }
        }
        sort(all(v));
        cout<<v[m-1]<<endl;
    }

}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
 
using namespace std;
 
#define NMAX 100
 
int main(){
 
    int hurui[200000]={0};
    int prime[100000];
    int table[300000]={0};
    int cnt=0;
    int cou;
 
    hurui[0]=1,hurui[1]=1;
    for(int i=2;i<200000;i++){
        if(hurui[i]==0){
            prime[cnt]=i;
            cnt++;
            for(int j=i;j<200000;j+=i){
                hurui[j]=1;
            }
        }
    }
 
    cou=cnt;
 
    int n,p;
 
    while(1){
        cin>>n>>p;
        if(n==-1&&p==-1) break;
        cnt=0;
        while(1){
            if(n<prime[cnt]) break;
            cnt++;
        }
        for(int i=0;i<300000;i++) table[i]=0;
        for(int i=cnt;i<cou;i++){
            for(int j=i;j<cou;j++){
                table[prime[i]+prime[j]]++;
            }
        }
        while(p>=0){
            p-=table[cnt];
            cnt++;
        }
        cout<<cnt-1<<endl;
    }
}

C++: #include <iostream>
#include <queue>
#include <vector>

using namespace std;

vector<bool> prime(100500,true);

int main(){
    prime[0] = prime[1] =false;
    for(int i=2;i*i<100500;i++){
        if(prime[i]){
            for(int j=2;j*i<100500;j++){
                prime[i*j]=false;
            }
        }
    }

    while(true){
        int n,p;
        cin >> n >> p;
        if(n==-1)break;
        vector<int> plist(50);
        int count=0;
        for(int i=n+1;count <50;i++){
            if(prime[i]){
                plist[count]=i;
                count++;
            }
        }

        priority_queue<int,vector<int>,greater<int> > mlist;
        for(int i=0;i<count;i++){
            for(int j=0;j<=i;j++){
                mlist.push(plist[i]+plist[j]);
            }
        }
        for(int i=0;i<p-1;i++){
            mlist.pop();
        }
        int ans=mlist.top();
        cout << ans << endl;
    }
    return 0;
}

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

const int NUM_P = 1000000;
vector<int> prime;
bool isPrime[NUM_P];
int N, P;

int make() {
  fill(isPrime, isPrime+NUM_P, true);
  isPrime[0] = isPrime[1] = false;
  for(int i = 2; i < NUM_P; ++i) {
    if(!isPrime[i]) continue;
    prime.push_back(i);
    for(int j = i*2; j < NUM_P; j += i) isPrime[j] = false;
  }
}

int solve() {
  int s = distance(prime.begin(), upper_bound(prime.begin(), prime.end(), N));
  vector<int> v;
  for(int i = 0; i < P; ++i) {
    for(int j = i; j < P; ++j) {
      v.push_back(prime[s+i] + prime[s+j]);
    }
  }
  sort(v.begin(), v.end());
  return v[P-1];
}

int main() {
  make();
  while(cin >> N >> P) {
    if(N == -1 && P == -1) break;
    cout << solve() << endl;
  }
  return 0;
}