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>
#define _ ios_base::sync_with_stdio(0);cin.tie(0);
#define REP(i,n) for(int i=0;i<(int)(n);i++)

using namespace std;
set<int> primes;
bool isPrime(int i){
  if(i<=1)return false;
  for(int p:primes){
    if(p>=i)break;
    if(i%p==0)return false;
  }
  return true;
}
int n,p;
void solve(){
  vector<int> m;
  auto a=primes.upper_bound(n);
  REP(i,p){
    auto b=a;
    REP(j,p){
      m.push_back((*a)+(*b));
      b++;
    }
    a++;
  }
  sort(m.begin(),m.end());
  cout<<m[p-1]<<endl;
}

int main(){ _;
  primes.insert(2);
  for(int i=3;i<120000;i+=2)
    if(isPrime(i))
      primes.insert(i);
  while(cin>>n>>p,(n&p)!=-1){
    solve();
  }
}

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

#define REP(i,s,n) for(int i=s;i<n;++i)
#define rep(i,n) REP(i,0,n)
#define SORT(c) sort((c).begin(),(c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
 
typedef long long ll;
typedef pair<int, int> ii;

int main() {
	
	ll n, p;
	vector<int> prime;
	vector<bool> check(150000);
	
	check[1] = check[0] = true;
	REP(i, 2, 150000){
		if(!check[i]) prime.push_back(i);
		for(int j = 2; i * j < 150000; j++){
			check[i * j] = true;
		}
	}
	
	//rep(i, prime.size()) cout << prime[i] << endl;
	//return 0;
	
	
	while(cin >> n >> p){
		if(n == -1 && p == -1) break;
		
		auto it = upper_bound(prime.begin(), prime.end(), n);
		vector<ll> tmp(p*p);
		rep(i, p){
			auto it2 = it;
			rep(j, p){
				tmp[i*p+j] = (ll)(*it) + *it2;
				it2++;
			}
			it++;
		}
		
		SORT(tmp);
		cout << tmp[p-1] << endl;
		
	}
	
	
	// your code goes here
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
int main(){
  int n,p,num[1000000];
  num[0]=0;
  for(int i=1;i<1000000;++i) num[i]=1;
  for(int i=2;i*i<1000000;++i)
    if(num[i-1])
      for(int j=2;i*j<1000000;++j) num[i*j-1]=0;
  while(cin>>n>>p&&n!=-1&&p!=-1){
    vector<int>add;
    int cnt=0,data[100];
    ++n;
    while(cnt!=p){
      if(num[n-1]){
	data[cnt]=n;
	++cnt;
      }
      ++n;
    }
    for(int i=0;i<p;++i)
      for(int j=i;j<p;++j)
	add.push_back(data[i]+data[j]);
    sort(add.begin(),add.end());
    cout<<add[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(500000);
	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, 300)
		{
			le = ri;
			repp(l,i, 300+i)
			{
				ans.push_back(*le + *ri);
				le++;
			}
			ri++;
		}
		sort(ans.begin(), ans.end());
		cout << ans[p-1] << endl;
	}
}

C++: #include <iostream>
#include <iomanip>
#include <sstream>
#include <stdio.h>
#include <list>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <algorithm>
#include <math.h>
#include <utility>
#include <string>
#include <ctype.h>
#include <cstring>
#include <cstdio>
#include <sstream>
#include <functional>

using namespace std;

#define FOR(i,k,n) for(int i = (k); i < (n); i++)
#define REP(i,n) FOR(i,0,n)
#define INF 114514810
#define ll long long
#define SORT(v) sort((v).begin(),(v).end())
//#define scanf scanf_s

int main()
{
	bool prime[200000];
	memset(prime, true, sizeof(prime));
	prime[0] = prime[1] = false;
	for (int i = 2; i*i < 200000; i++)
	{
		if (prime[i] == true)
		{
			for (int j = 2; i*j < 200000; j++)
			{
				prime[i*j] = false;
			}
		}
	}

	int n, p;
	while (cin >> n >> p)
	{
		if (n == -1) break;
		vector<int> v, s;

		for (int i = n+1; v.size() < 100; i++)
		{
			if (prime[i] == true) v.push_back(i);
		}
		REP(i, 100)for (int j = i; j < 100; j++)
		{
			s.push_back(v[i] + v[j]);
		}
		SORT(s);
		cout << s[p - 1] << endl;

	}
	return 0;
}