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>
using namespace std;

using ll=long long;
#define int ll

#define FOR(i,a,b) for(int i=int(a);i<int(b);i++)
#define REP(i,b) FOR(i,0,b)

int read(){
  int i;
  scanf("%lld",&i);
  return i;
}

bool is_prime(int n){
  if(n==0||n==1) return false;
  if(n==2) return true;
  for(int i=2;i*i<=n;i++){
    if(n%i==0) return false;
  }
  return true;
}

signed main(){
  while(true){
    int N=read(),P=read();
    if(N==-1&&P==-1) break;
    vector<int> prime;
    vector<int> matsuzaki;
    ++N;
    while(1){
      if(is_prime(N)){
        prime.push_back(N);
        REP(j,prime.size()){
          matsuzaki.push_back(prime[j]+N);
        }
        if(matsuzaki.size()>=P){
          break;
        }
      }
      N++;
    }
    // cerr << "----prime----" << endl;
    // REP(i, prime.size()) {
    //   cerr << prime[i] << endl;
    // }
    sort(matsuzaki.begin(),matsuzaki.end());
    // cerr << "----matsuzaki----" << endl;
    // REP(i, matsuzaki.size()) {
    //   cerr << matsuzaki[i] << endl;
    // }
    cout << matsuzaki[P - 1] << endl;
  }    
}

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

#define rep(i, n) for(int i = 0; i < n; i++)

typedef long long ll;
using namespace std;
int mod = 1000000007;

int main(void){
    int N, P;
    vector<int> prime_ls;
    bool pr[200000];
    rep(i, 200000) pr[i] = true;
    pr[1] = false;
    for(int i = 2; i < 1000; i++){
        for(int j = (i << 1); j < 200000; j+=i){
            pr[j] = false;
        }
    }
    for(int i = 2; i < 200000; i++) if(pr[i]) prime_ls.push_back(i);

    vector<int> ans;
    while(true){
        cin >> N >> P;
        if(N == -1) break;
        int work[P*P];
        rep(i, P*P) work[i] = mod;
        int idx = 0;
        while(prime_ls[idx] <= N) idx++;
        for(int i = idx; i < idx+P; i++){
            for(int j = i; j < idx+P; j++){
                work[(i-idx)*P+(j-idx)] = prime_ls[i] + prime_ls[j];
            }
        }
        sort(work, work + (P*P));
        //rep(i, 100) cout << work[i] << " "; cout << endl;
        ans.push_back(work[P-1]);
    }
    rep(i, ans.size()) cout << ans[i] << endl;
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
#define MAX_N 210000
#define MUL 2

/*エラトステネスの篩*/
void Eratosthenes(int *pri) {
  for(int i = 2; i < MAX_N; i++)
    pri[i] = 1;

  for(int i = 2; (i * i) < MAX_N; i++) {
    if(pri[i] == 1) {
      for(int j = (i * 2); j < MAX_N; j+=i)
        pri[j] = 0;
    }
  }
}

int matsuzaki(int N, int P, int *pri) {
  vector<int> sum;
  vector<int> prime;
  int count = 0;

  for(int i = N + 1;; i++) {
    if(pri[i] == 1) {
      prime.push_back(i);
      count++;
    }
    if(count > P)
      break;
  }

  count = 0;

  for(int i = 0; i < P; i++) {
    for(int j = i; j < P; j++) {
      sum.push_back(prime[i] + prime[j]);
      count++;
    }
  }

  sort(sum.begin(), sum.end());
  prime.clear();

  return sum[P-1];
}

int main() {
  int N;
  int P;
  int pri[MAX_N];
  pri[0] = 0;
  pri[1] = 0;

  Eratosthenes(pri);

  while(1) {
    cin >> N >> P;
    if(N == -1 && P == -1)
      break;

    cout << matsuzaki(N, P, pri) << endl;
  }
  return 0;
}

C++: #include<stdio.h>
#include<iostream>
#include<string>
#include<algorithm>
#include <vector>
#include<math.h>


using namespace std;

bool f[1000002];

int main(){
	for(int i=3;i<1000001;i+=2){f[i]=true;
		for(int j=3;j*j<=i;j+=2)
			if(i%j==0)f[i]=false;
	}
	f[2]=true;
	int n,p;
	while(1){
		cin>>n>>p;if(n==-1&&n==p)break;

		int r=0;
		int q[10001]={};
		int x=0;
		int y=n+1;
		while(1){
			if(f[y]==true)x++;
			if(x==p)break;
			y++;
		}
		n++;
		 vector<int> anslist;
		 for(int i=n;i<=y;i++)
			for(int j=i;j<=y;j++)
			{
				if(f[i]==true&&f[j]==true){
					anslist.push_back(i+j);
				
				//cout<<i<<" "<<j<<endl;
				}
			}
			sort(anslist.begin(),anslist.end());
/*
		for(int i=n;i<=y;i++)
			for(int j=i;j<=y;j++)
			{
				if(f[i]==true&&f[j]==true){
				q[r]=i+j;r++;
				}
			}

		/*	
		sort(q,q+r);
		for(int i=0;i<r;i++)
		cout<<q[i]<<endl;

		cout<<q[p-1]<<endl;*/
			  cout << anslist[p-1] << endl;

	}
	
	return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string> 
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

int min_prime(int n);
int isprime(int n);

int main()
{
	int n, p;
	while(1){
		cin >> n >> p;
		if(n == -1 && p == -1) break;
		int prime_array[1000] = {0}, sum_array[10000] = {0};
		if(isprime(n)) prime_array[0] = n;
		else prime_array[0] = min_prime(n);
		for(int i = 0; i < 100; i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < 50; i++){
			for(int j = i; j < 50; j++){
				sum_array[k] = prime_array[i] + prime_array[j];
				k++;
			}
		}
		sort(sum_array, sum_array+k);
		cout << sum_array[p - 1] << endl;
	}
	return 0;
}

int min_prime(int n)
{
	int i = 1;
	while(1){
		if(isprime(n + i)) return n + i;
		else i++;
	}
}

int isprime(int n)
{
	int ans;
	if(n == 0 || n == 1) ans = 0;
	else if(n == 2) ans = 1;
	else {
		for(int i = 2; i < n; i++){
			if(i * i > n) ans = 1;
			else if(n % i == 0){
				ans = 0;
				break;
			}
		}
	}
	return ans;
}