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 <sstream>
#include <vector>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <utility>

#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 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 prime[150000];
bool is_prime[150000];
vector<ll> v;

void sieve(){
  int p=0;
  rep(i,150000)is_prime[i]=true;
  is_prime[0]=is_prime[1]=false;
  REP(i,2,150000){
    if(is_prime[i]){
      prime[p++]=i;
      for(int j=2*i;j<150000;j+=i)is_prime[j]=false;
    }
  }
  //rep(i,50)cout<<"DEBUG "<<prime[i]<<endl;
}

void solve(int n,int p){
  ll data[11000];
  int x=0;
  while(prime[x]<=n){
    //cout<<x<<" "<<prime[x]<<endl;
    x++;
  }
  int cnt=0;
  REP(i,x,x+p){
    REP(j,i,x+p){
      data[cnt]=(prime[i]+prime[j]);
      cnt++;
    }
  }
  sort(data,data+cnt);
  //rep(i,p)cout<<i+1<<" "<<v[i]<<endl;
  cout<<data[p-1]<<endl;
}

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

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

#define REP(i, n) for(int i = 0; i < (int) (n); i++)
#define ALL(v) (v).begin(), (v).end()
#define INF 1e9

using namespace std;

vector<int> prime;

void make_prime(){
  bool is_prime[101000];
  REP(i, 101000) is_prime[i] = true;
  REP(i, 101000){
    if(i == 0 or i == 1) is_prime[i] = false;
    if(!is_prime[i]) continue;
    REP(j, 101000){
      if(j == 0 or j == 1) continue;
      if(i * j > 101000) break;
      is_prime[i * j] = false;
    }
  }
  REP(i, 101000) if(is_prime[i]) prime.push_back(i);
}

int main(){
  int n, p;
  make_prime();
  while(cin >> n >> p and n + p != -2){
    int from = 0;
    vector<int> sums;
    REP(i, prime.size()) if(prime[i] > n) { from = i; break; }
    REP(i, 100) REP(j, i+1){
      if(from + i >= prime.size()) continue;
      sums.push_back(prime[from+i] + prime[from+j]);
    }
    sort(ALL(sums));
    cout << sums[p-1] << endl;
  }
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;

const int MAX_N = 1000000;

int prime[MAX_N];
bool is_prime[MAX_N + 1];

void eratos(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;
        }
    }
}

int main() {
    eratos(MAX_N);

    int N, P;

    while (cin >> N >> P, (N != -1 and P != -1)) {
        vector<int> t(100);
        int cnt = 0;

        for (int i=N+1; i<MAX_N; ++i) {
            if (is_prime[i]) { t[cnt++] = i; }
            if (cnt >= 100) break;
        }

        vector<int> tt(10001);
        cnt=0;
        rep(i, 100) {
            for (int j=i; j<100; ++j) {
                tt[cnt++] = t[i] + t[j];
            }
        }

        sort(tt.begin(), tt.end());

        cout << tt[P-1] << endl;

    }

}

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

using namespace std;

int main(){
	vector<int> data;
	data.push_back(2);
	data.push_back(3);
	for(int i=4;i<1000000;i++){
		bool flag = true;
		for(int j=2;j*j<=i;j++){
			if(i%j==0){
				flag = false;
			}
		}
		if(flag){
			data.push_back(i);
		}
	}

	while(true){
		int n,p;
		cin >> n >> p;
		if(n == -1 && p == -1){
			break;
		}

		int count = 0;
		while(data[count] <= n){
			count++;
		}
		vector<int> anslist;
		for(int i=count;i<count+70;i++){
			for(int j=i;j<count+70;j++){
				anslist.push_back(data[i]+data[j]);
			}
		}
		sort(anslist.begin(),anslist.end());

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

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

#define all(c) (c).begin(),(c).end()

using namespace std;

vector<int>p,v;
bool fg[101000];

int main(void){

  for(int i=2;i*i<101000;i++){
    if(!fg[i]){
      for(int j=i*i;j<101000;j+=i){
	fg[j]=true;
      }
    }
  }
  for(int i=2;i<101000;i++)
    if(!fg[i])p.push_back(i);

  int N,P;
  while(cin >> N >> P,0<=N && 0<=P){
    int b = upper_bound(all(p),N) - p.begin();
    int psize = p.size();
    v.clear();
    for(int i=b;i-b<P && i<psize;i++){
      for(int j=i;j-i<P && j<psize;j++){
	v.push_back(p[i]+p[j]);
      }
    }
    sort(all(v));
    cout << v[P-1] << endl;
  }
  
  return 0;
}