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<string>
#include<cmath>
#include<queue>
#include<vector>
#include<functional>
using namespace std;
bool a[200000];
int main() {
	fill(a, a + 200000, true);
	a[0] = false; a[1] = false;
	for (int i = 0; i < 200000; i++) {
		if (a[i]) {
			int j = 2;
			while (i*j < 200000) {
				a[i*j] = false;
				j++;
			}
		}
	}
	int n, p;
	while (cin >> n >> p&&n != -1 && p != -1) {
		int sum = 0;
		int b[1000];
		for (int i = n; i < 200000 && sum <= p; i++) {
			if (a[i]) {
				b[sum] = i;
				sum++;
			}
		}
		int c[10000];
		int sum2 = 0;
		for (int i = 0; i < sum; i++) {
			for (int j = i; j < sum; j++) {
				c[sum2] = b[i] + b[j];
				sum2++;
			}
		}
		sort(c, c + sum2);
		cout << c[p - 1] << endl;
	}
}

C++: 
#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;

int prime[1000000];

int init()
{
  memset(prime, -1, sizeof prime);
  prime[0] = prime[1] = 0;
  for(int i = 2; i < 1000000; i++)
  {
    if(prime[i] != -1)
      continue;
    prime[i] = 1;
    for(int j = i + i; j < 1000000; j += i)
      prime[j] = 0;
  }
}

int main()
{
  init();
loop:
  int n, p;
  vector<int> prm;
  vector<int> m;
  cin >> n >> p;
  if(n == -1)
    return 0;
  int i = n;
  for(int cnt = 0; cnt < 100; cnt++)
  {
    i++;
    while(!prime[i])
      i++;
    prm.push_back(i);
  }
  for(int i = 0; i < 100; i++)
    for(int j = i; j < 100; j++)
      m.push_back(prm[i] + prm[j]);
  sort(m.begin(), m.end());
  cout << m[p - 1] << endl;
  goto loop;
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
using namespace std;
int n,p;
bool f(int a)
{
	if(a<2)return 0;
	for(int i=2;i*i<=a;i++)if(a%i<1)return 0;
	return 1;
}
main()
{
	while(cin>>n>>p,n>=0)
	{
		vector<int>P;
		int u=p;
		for(int i=n+1;u;i++)
		{
			if(f(i))
			{
				u--;
				P.push_back(i);
			}
		}
		vector<int>a;
		for(int i=0;i<p;i++)for(int j=i;j<p;j++)a.push_back(P[i]+P[j]);
		sort(a.begin(),a.end());
		cout<<a[p-1]<<endl;
	}
}

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

using namespace std;

int isPrime(int num) {
  if(num < 2) {
    return 0;
  }
  for(int i=2; i<=sqrt(num); i++) {
    if(num%i == 0) {
      return 0;
    }
  }
  return 1;
}

int main() {
  int n, p;
  while(cin>>n>>p && (n!=-1 && p!=-1)) {
    vector<int> ansVec;
    vector<int> primeVec;
    for(int i=n+1; primeVec.size()<100; i++) {
      if(isPrime(i)) {
	primeVec.push_back(i);
	//cout<<i<<" ";
      }
    }
    while(ansVec.size() < p) {
      for(int i=0; i<100; i++) {
	for(int j=i; j<100; j++) {
	  ansVec.push_back(primeVec[i]+primeVec[j]);
	}
      }
    }
    sort(ansVec.begin(), ansVec.end());
    /*
    cout<<endl;
    for(int i=0; i<5; i++) {
      cout<<ansVec[i]<<" ";
    }
    cout<<endl;
    */
    cout<<ansVec[p-1]<<endl;
  }
}

C++: #include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<vector>
#include<string>
#include<sstream>
#include<cmath>
#include<numeric>
#include<map>
#include<stack>
#include<queue>
#include<cassert>
using namespace std;
int inf = 1000000000;

vector<bool> isPrime(int n){
  vector<bool> ret(n+1, true);
  ret[0] = false;
  ret[1] = false;
  for(int i=2; i<=sqrt(n); i++){
    if( !ret[i] ) continue;
    for(int j=i+i; j<n; j+=i){
      ret[j] = false;
    }
  }
  return ret;
}

int main(void) {

  vector<bool> prime = isPrime(1000000);
  int n, p;
  while(cin >> n >> p){
    if( n == -1 && p == -1 ) break;

    int cnt = 0;
    vector<int> a;
    for(int i=n+1; i<=prime.size(); i++){
      if( cnt > 100 ) break;
      if( !prime[i] ) continue;
      cnt++;
      int tmp = 0;
      for(int j=i; j<=prime.size(); j++){
        if( tmp > 100 ) break;
        if( !prime[j] ) continue;
        tmp++;
        a.push_back( i+j );
      }
    }
    sort(a.begin(), a.end());
    cout << a[p-1] << endl;

  }



  return 0;
}


// EOF

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

using ll=long long;
#define int ll

#define FOR(i,a,b) for(int i=int(a);i<int(b);i++)
#define REP(i,b) FOR(i,0,b)

int read(){
  int i;
  scanf("%lld",&i);
  return i;
}

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

signed main(){
  while(true){
    int N=read(),P=read();
    if(N==-1&&P==-1) break;
    vector<int> prime;
    vector<int> matsuzaki;
    ++N;
    while(1){
      if(is_prime(N)){
        prime.push_back(N);
        REP(j,prime.size()){
          matsuzaki.push_back(prime[j]+N);
        }
        if(prime.size()>=P){
          break;
        }
      }
      N++;
    }
    // cerr << "----prime----" << endl;
    // REP(i, prime.size()) {
    //   cerr << prime[i] << endl;
    // }
    sort(matsuzaki.begin(),matsuzaki.end());
    // cerr << "----matsuzaki----" << endl;
    // REP(i, matsuzaki.size()) {
    //   cerr << matsuzaki[i] << endl;
    // }
    cout << matsuzaki[P - 1] << endl;
  }    
}