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;
    }
  }
  //cout<<"p: "<<p<<"  max: "<<prime[p-1]<<endl;
}

/*
int binary_search(int n){
  int l=0,r=111111;
  int i;
  while(r-l>=1){
    i=(r+l)/2;
    if(prime[i]==n)return i;
    else if(prime[i]>n) l=i+1;
    else r=i;
  }
  if(prime[i]<n)i++;
  return i;
}
*/
int straight_search(int n){
  for(int i=0;i<110000;i++){
    if(prime[i]>n)return i;
  }
  return 0;
}

void matuzaki(int n,int p){
  vi v;
  v.clear();
  int near=straight_search(n);
  //cout<<"near: "<<near<<"   prime:"<<prime[near]<<endl;
  for(int i=near;i<=near+500;i++){
    for(int j=i;j<=near+500;j++){
      v.pb(prime[i]+prime[j]);
    }
  }
  sort(all(v));
  //rep(i,p*p)cout<<i<<":  "<<v[i]<<endl;
  cout<<v[p-1]<<endl;
}

int main(){
  int n,p;
  prime_judge();
  while(cin>>n>>p){
    if(n==-1&&p==-1)break;
    matuzaki(n,p);
  }
  return 0;
}

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

bool seive[300001];
vector<int> matuzakiList;

void init(){
  for(int i = 0; i <= 300000; i++) seive[i] = true;
  seive[0] = seive[1] = false;
  for(int i = 2; i * i <= 300000; i++){
    for(int j = i * i; j <= 300000; j = j + i) seive[j] = false;
  }
}

int matuzakiNumber(int N, int P){
  int prime[30] = {0}, cnt = 0;
  for(int i = N + 1; cnt != 30; i++){
    if(seive[i]) prime[cnt++] = i;
  }
  for(int i = 0; i < 30; i++){
    for(int j = i; j < 30; j++){
      int ml = prime[i] + prime[j];
      matuzakiList.push_back(ml);
    }
  }
  sort(matuzakiList.begin(), matuzakiList.end());
  return matuzakiList[P-1];
}

int main(void){
  init();
  int N, P;
  while(cin >> N >> P && N != -1 && P != -1){
    matuzakiList.clear();
    cout << matuzakiNumber(N, P) << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int a[100000]={2,3},i,j,k,c=2,b[100002][101],q,w[450];
int main(){
  for(i=4;i<150000;i++){
    for(k=1,j=2;j*j<=i;j++){
      if(i%j==0){k=0;break;}
    }
    if(k)a[c++]=i;
  }k=0;
  for(i=0;i<=100000;i++){
    if(i>=a[k])k++;
    for(q=0,j=k;j<k+20;j++){
      for(c=j;c<j+20;c++){
        w[q++]=a[j]+a[c];
      }
    }
    sort(w,w+q-1);
    for(c=0;c<=100;c++)b[i][c]=w[c];
  }
  while(cin>>i>>j){
    if(i<0)break;
    cout<<b[i][j-1]<<endl;
  }
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
typedef vector<int> vi;
#define loop(i,a,b) for(int i=(a); i<int(b); i++)
#define rep(i,b) loop(i,0,b)
#define all(c) (c).begin(), (c).end()

int const N = 10000000;
bool isp[N];
int ps[N / 2];
int c = 0;
void eratos(){
    rep(i, N) isp[i] = true;
    isp[0] = isp[1] = false;
    for (int i = 2; i < N; i++){
        if (!isp[i]) continue;
        ps[c++] = i;
        for (int j = i + i; j < N; j += i){
            isp[j] = false;
        }
    }
}

int solve(int n, int p){
    auto it = upper_bound(ps, ps + c, n);
    vi v(p*p, 1 << 30);
    rep(i, p)loop(j, i, p){
        v[i * p + j] = *(it + i) + *(it + j);
    }
    sort(all(v));
    return v[p - 1];
}

int main(){
    eratos();
    int n, p;
    while (cin >> n >> p && n!=-1 && p!=-1){
        cout << solve(n, p) << endl;
    }
}