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>
#include <vector>
#include <algorithm>
#include <iostream>

#define rep(i,n) for(int i=0;i<(n);i++)
#define loop(i,x,n) for(int i=(x);i<(n);i++)
#define all(v) (v).begin(),(v).end()
#define int long long
using namespace std;
const int MOD=1e9+7;
const int INF=1e15;
template<typename T> void cmax(T &a, T b) {a = max(a, b);}
template<typename T> void cmin(T &a, T b) {a = min(a, b);}

const int MAX_N=200005;
bool isPrime[MAX_N];
void eratos(){
  for(int i=0;i<MAX_N;i++)isPrime[i]=true;
  isPrime[0]=isPrime[1]=false;
  for(int i=0;i<MAX_N;i++){
    if(isPrime[i]){
      for(int j=i+i;j<MAX_N;j+=i){
        isPrime[j]=false;
      }
    }
  }
}

signed main(){
  eratos();
  int n,p;
  while(cin>>n>>p){
    if(n==-1&&p==-1)break;
    vector<int> ans;
    int tmpp=101;
    int s=n+1;
    while(tmpp){
      if(isPrime[s]){
        int tmpq=101;
        int t=s;
        while(tmpq){
          if(isPrime[t]){
            ans.push_back(s+t);
            tmpq--;
          }
          t++;
        }
        tmpp--;
      }
      s++;
    }
    sort(all(ans));

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


 return 0;
}

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

using namespace std;

vector<int> setPrime(int N)
{
	vector<int> v;
	if (N < 2)
	{
		v.push_back(2);
		N = 2;
	}
	for (int i = N + 1; i <= 1000000; i++)
	{
		bool flag = false;
		for (int j = 2; j * j <= i; j++)
		{
			if (i % j == 0)
			{
				flag = true;
				break;
			}
		}

		if (!flag)
		{
			v.push_back(i);
		}
	}

	return v;
}
int main()
{
	int N, P;
	while (cin >> N >> P && N != -1 && P != -1)
	{
		vector<int> primeNum;
		primeNum = setPrime(N);
		vector<int> primeSum;
		for (int i = 0; i < P; i++)
		{
			for (int j = i; j < P; j++)
			{
				primeSum.push_back(primeNum.at(i) + primeNum.at(j));
			}
		}
		sort(primeSum.begin(),primeSum.end());
		cout << primeSum.at(P - 1) << endl;
	}
	return 0;
}

C++: // clang-format off
#include <bits/stdc++.h>
#define int long long
#define main signed main()
// #define main int main()
#define loop(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) loop(i, 0, n)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define prec(n) fixed << setprecision(n)
#define stlice(from, to) substr(from, (to) - (from) + 1)
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
using namespace std;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<string> vs;
typedef vector<pii> vpii;
typedef vector<vi> vvi;
typedef vector<vb> vvb;
typedef vector<vpii> vvpii;
const int INF = sizeof(int) == sizeof(long long) ? 1000000000000000000LL : 1000000000;
const int MOD = 1000000007;
const double PI = acos(-1);
template<typename A, typename B> bool cmin(A &a, const B &b) { return a > b ? (a = b, true) : false; }
template<typename A, typename B> bool cmax(A &a, const B &b) { return a < b ? (a = b, true) : false; }
bool odd(const int &n) { return n & 1; }
bool even(const int &n) { return !odd(n); }
template<typename V> typename V::value_type sum(const V &v) { return accumulate(all(v), 0); }
void solve();
main { solve(); return 0; }
// clang-format on

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

int f(int n, int p) {
  int l = n + 1;
  vi v;
  v.reserve(100);
  for (int i = n + 1, x = 0; x < 100; i++) {
    if (isPrime(i)) v.pb(i), x++;
  }
  vi w;
  w.reserve(10000);
  rep(i, 100) loop(j, i, 100) w.pb(v[i] + v[j]);
  sort(all(w));
  return w[p - 1];
}

void solve() {
  int n, p;
  while (cin >> n >> p, n >= 0) cout << f(n, p) << endl;
}

C++: #include<bits/stdc++.h>
#define rep(i,n) for(int i=0; i<n; i++)
using namespace std;
bool isPrime(int x){
    if(x < 2) return false;
    if(x == 2) return true;
    if(x % 2 == 0) return false;
    for(int i=3; i*i<=x; i+=2){
        if(x % i == 0) return false; 
    }
    return true;
}
int main(){
    int n,p;
    while(cin >> n >> p){
        if(n == -1 && p == -1) break;
        vector<int> vec;
        for(int i=n+1; i<=n+1000; i++){
            if(isPrime(i)){
                for(int j=i; j<=n+1000; j++) if(isPrime(j)) vec.push_back(i+j);
            }
        }
        sort(vec.begin(),vec.end());
        cout << vec[p-1] << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){

  vector <int> so,sum;
  int a[110001]={0},from,n,p,i,j;
  
   for(i=2;i<=110000;i++){
    if(a[i]==0){
      so.push_back(i);
      for(j=i;j<=110000;j+=i) a[j]=1;
    }
   }
   //for(i=0;i<20;i++) cout<<so[i]<<endl;
   while(cin>>n>>p,n!=-1){
  from=0;
  for(i=0;n>=so[i];i++) from++;
  //cout<<from<<endl;
  sum.clear();
  for(i=from;i<from+p;i++) for(j=i;j<from+p;j++) sum.push_back(so[i]+so[j]);
  sort(sum.begin(),sum.end());

  cout<<sum[p-1]<<endl;
   }
  
  return 0;

}