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[13000];
bool is_prime[150000];

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;
    }
  }
}

void solve(int n,int p){
  vi v;
  int x=0;
  while(prime[x]<=n){
    x++;
  }
  
  REP(i,x,x+p){
    REP(j,i,x+p){
      v.push_back(prime[i]+prime[j]);
    }
  }
  sort(all(v));
  cout<<v[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, a, n) for(int i = a; i < n; i++)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define o(a) cout << a << endl
#define int long long
#define fi first
#define se second
using namespace std;
typedef pair<int, int> P;

const int MAX_N = 200010;
int prime[MAX_N];
bool is_prime[MAX_N + 1];
void sieve(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;
        }
    }
}

signed main(){
    int n, p;
    sieve(MAX_N);
    while(1){
        cin >> n >> p;
        if(n + p == -2) break;
        int id = -1;
        rep(i, 0, MAX_N) if(prime[i] > n){ id = i; break;}
        vector<int> d;
        rep(i, 0, 100) rep(j, i, 100) d.push_back(prime[id + i] + prime[id + j]);
        sort(all(d));
        cout << d[p - 1] << endl;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;

int main() {
  vector<int> primes{2};  
  for ( int i = 3; i < 102000; i += 2 ) {
    bool flag = true;
    for ( int j = 3; j <= sqrt(i); j += 2 ) {
      if ( i%j == 0 ) {
	flag = false;
	break;
      }
    }
    if ( flag ) primes.push_back(i);
  }

  int N, P;
  while ( cin >> N >> P, N >= 0 ) {
    int p = upper_bound(primes.begin(), primes.end(), N)-primes.begin();
    vector<int> dat;
    for ( int i = p; i < p+110; i++ ) {
      for ( int j = i; j < p+110; j++ ) {
	dat.push_back(primes[i]+primes[j]);	
      }	
    }

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

    cout << dat[P-1] << endl;    
  }
  
  return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include<cstdio>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<utility>
#include<iomanip>
#include<vector>
#include<string>
#include<queue>
#include<stack>
#include<map>
#include<list>
#include<set>
#include<stdlib.h>
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define repp(i,k,n) for(int i=k;i<(int)n;i++)
using namespace std;
const int dx[4] = { 0, 1, 0, -1 }, dy[4] = { 1, 0, -1, 0 };
const int dX[8] = { 0, 1, 1, 1, 0, -1, -1, -1 }, dY[8] = { 1, 1, 0, -1, -1, -1, 0, 1 };
vector<long long> Prime;
void SieveOfEratosthenes(long long e) //setup vector<long long>Prime(~x)
{
	bool *x=new bool[e];
	for (long long i = 0; i <= e; i++)x[i] = false;
	for (long long i = 2; i <= e; i++)
	{
		if (x[i]);
		else
		{
			Prime.push_back(i);
			for (long long l = i; l <= e; l += i)x[l] = true;
		}
	}
	return;
}
struct XY
{
	int x;
	int y;
};
int in()
{
	int x;
	cin >> x;
	return x;
}
/*
(char)'1' - (int)48 = (int)1;
???1111181
*/
////////////////////////////////////////////////////



int main()
{
	SieveOfEratosthenes(300000);
	int n,p;
	while (cin>>n>>p&&n!=-1)
	{
		vector<long long>::iterator now=lower_bound(Prime.begin(),Prime.end(),n),ri,le;
		vector<long long > ans;
		ri = now;
		le = now;
		rep(i, 100)
		{
			le = ri;
			repp(l,i, 100+i)
			{
				ans.push_back(*le + *ri);
				le++;
			}
			ri++;
		}
		sort(ans.begin(), ans.end());
		cout << ans[p-1] << endl;
	}
}