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;

#define FOR(i, a, n) for(int i = (a); i < (n); i++)
#define REP(i, n) for(int i = 0; i < (n); i++)
#define print(a) cout << a << "\n"
#define ALL(obj) (obj).begin(), (obj).end()
#define debug(x) cerr << #x << ": " << x << '\n'

#define MAX 250000



int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int prim[MAX];
  REP(i, MAX) {
    prim[i] = 1;
  }
  prim[0] = 0;
  prim[1] = 0;
  FOR(i, 2, sqrt(MAX)) {
    if(prim[i] == 0) continue;
    FOR(j, 2, MAX) {
      if(i * j > MAX) {
        break;
      }
      prim[i * j] = 0;
    }
  }

  vector<int> p;
  REP(i, MAX) {
    if(prim[i] == 1) {
      p.push_back(i);
    }
  }

  bool flag = true;
  int N, P;

  while(true){
    int count = 0;
    cin >> N >> P;
    if(N + P == -2) break;

    vector<int> sum;

    REP(i, p.size()) {
      if(count > 15){
        break;
      }
      if(p[i] > N) {
        count++;
        FOR(j, i, P + i) {
          sum.push_back(p[i] + p[j]);
        }
      }
    }

    sort(ALL(sum));

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

  return 0;
}

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

using namespace std;

#define N 1000000
#define all(p) p.begin(),p.end()
bool primes[N];

int main() {
    vector<int> prime;
    
    primes[0] = primes[1] = 1;

    for (int i=2;i<N;i++) {
        if(!primes[i]) {
            for (int j=i;j<N;j+=i) primes[j] = 1;
            prime.push_back(i);
        }
        if(prime.size() == 100100) break; 
    }
    int n,p;
    while(cin >> n >> p && !(n==-1&&p==-1) ) {
        int i;
        vector<int> mp;
        for (i=0;prime[i]<=n;i++);
        for (int j=i;j<i+25;j++)  for(int k=j;k<i+25;k++) 
                mp.push_back(prime[j]+prime[k]);
        sort(all(mp));
        cout << mp[p-1] << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<map>
#include<set>
#include<utility>
#include<vector>
#include<cmath>
#include<cstring>
#include<cstdio>
#include<time.h>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mp make_pair
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
const double EPS=1e-10;
const int inf=1e8;
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
#define ma 2000000
bool sosu[ma]={1,1,0};
int main(){
	for(int i=4;i<ma;i+=2)sosu[i]=1;
	for(int j=3;j<ma;j+=2)if(!sosu[j])
	for(int i=j*3;i<ma;i+=j*2)sosu[i]=1;
	
	int a,b;
	while(cin>>a>>b,a+1){
		int m=0;
		a++;
		vi out;
		int co=-1;
		loop(i,a,1e9){
			if(!sosu[i])co++;
			if(co==b+1){m=i;break;}
		}
		loop(i,a,m){
			if(sosu[i])continue;
			loop(j,i,m)if(!sosu[j])out.pb(i+j);
		}
		sort(all(out));
		cout<<out[b-1]<<endl;
	}
}

C++: #include<iostream>
#include<vector>
#include<cmath>
#define MAX 1000000
using namespace std;

void eratos ( int n, vector<int> &v){
    bool prime[MAX+1];
    for ( int i = 0; i <= n; i++ ) prime[i] = false;
    for ( int i = 3; i <= n; i += 2 ) prime[i] = true;
    prime[2] = true;
    int limit = (int)sqrt((double)n) + 1;
    for ( int i = 3; i <= limit; i += 2 ){
	if ( !prime[i] ) continue;
	for ( int j = i + i; j <= n; j += i ) prime[j] = false;
    }
    for ( int i = 0; i <=n; i++ ) if (prime[i]) v.push_back(i);
}

main(){
    int N, P;
    vector<int> primes;
    eratos(MAX, primes);

    int k;
    while(1){
	cin >> N >> P;
	if ( N == -1 && P == -1 ) break;
	int s = distance(primes.begin(), upper_bound(primes.begin(), primes.end(), N));

	vector<int> v;
	for ( int i = s; i < s+P; i++ ){
	    for ( int j = i; j < s+P; j++ ){
		v.push_back(primes[i] + primes[j]);
	    }
	}
	sort(v.begin(), v.end());
	cout << v[P-1] << endl;
    }
}

C++: #include "bits/stdc++.h"

using namespace std;

typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;

#define dump(x)  cerr << #x << " = " << (x) << endl
#define rep(i,n) for(int i=0;i<(n);i++)
#define all(a)  (a).begin(),(a).end()
#define pb push_back

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


vi solvePrime(int n){
    vi ret;
    int c=0;
    for(int i=n+1;;i++){
        if(isPrime(i)){
            ret.pb(i);
            c++;
        }
        if(c>=101)break;
    }
    return ret;
}



int main(){
    int n,p;
    while(cin>>n>>p){
        if(n==-1 && p==-1)break;
        
        vi prime;
        prime=solvePrime(n);
        
        vi result;
        
        int len=prime.size();
        rep(i,len){
            for(int j=i;j<len;j++){
                result.pb(prime[i]+prime[j]);
            }
        }
        sort(all(result));
//        rep(i,len)cout<<result[i]<<endl;
        
        cout<<result[p-1]<<endl;
    }

    
    return 0;
}