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 <vector>
#include <algorithm>
using namespace std;

bool seive[300001];
vector<int> matuzakiList;

void init(){
  for(int i = 0; i <= 300000; i++) seive[i] = true;
  seive[0] = seive[1] = false;
  for(int i = 2; i * i <= 300000; i++){
    for(int j = i * i; j <= 300000; j = j + i) seive[j] = false;
  }
}

int matuzakiNumber(int N, int P){
  int prime[30] = {0}, cnt = 0;
  for(int i = N + 1; cnt != 30; i++){
    if(seive[i]) prime[cnt++] = i;
  }
  for(int i = 0; i < 30; i++){
    for(int j = i; j < 30; j++){
      int ml = prime[i] + prime[j];
      matuzakiList.push_back(ml);
    }
  }
  sort(matuzakiList.begin(), matuzakiList.end());
  return matuzakiList[P-1];
}

int main(void){
  init();
  int N, P;
  while(cin >> N >> P && N != -1 && P != -1){
    matuzakiList.clear();
    cout << matuzakiNumber(N, P) << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <sstream>
#include <fstream>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cmath>
using namespace std;

typedef long long Int;

const int SQRTN = 1<<16; // upperbound of sqrt(H)
vector<Int> segmentSieve(Int L, Int H) {
  static int p[SQRTN], lookup = 0;
  if (!lookup) {
    for (int i = 2; i < SQRTN; ++i) p[i] = i;
    for (int i = 2; i*i < SQRTN; ++i)
      if (p[i])
        for (int j = i*i; j < SQRTN; j += i)
          p[j] = 0;
    remove(p, p+SQRTN, 0);
    lookup = 1;
  }
  vector<Int> table(H - L);
  for (Int i = L; i < H; ++i) table[i - L] = i;
  for (int i = 0, j; p[i] * p[i] < H; ++i) { // O( \sqrt(H) )
    if (p[i] >= L) j = p[i] * p[i];
    else if (L % p[i] == 0) j = L;
    else                    j = L - (L % p[i]) + p[i];
    for (; j < H; j += p[i]) table[j-L] = 0;
  }
  return table;
}

int main() {
    int n, p;
    while ( cin >> n >> p ) {
        if ( n == -1 && p == -1 ) break;
        if ( n == 0 ) n = 1;
        vector <Int> T = segmentSieve( n+1, n+5000 );
        vector <Int> P;
        for ( int i = 0; i < (int)T.size(); i++ ) {
            if ( T[i] != 0 ) {
                P.push_back( n+i+1 );
            }
        }
        int N = P.size();
        vector <Int> X;
        for ( int i = 0; i < N; i++ ) {
            for ( int j = i; j < N; j++ ) {
                X.push_back( P[i] + P[j] );
            }
        }
        sort( X.begin(), X.end() );
        cout << X[p-1] << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<algorithm>
using namespace std;
int isPrime(int x){
  int i;
  if(x < 2)return 0;
  else if(x==2)return 1;
  if(x%2 == 0)return 0;
  for(i=3 ; i*i <= x ; i+=2){
    if(x%i == 0)return 0;
  }
  return 1;
}
int main(){
  
  int N,P;
  
  while(1){
    
    cin >>N>>P;
    if(N==-1 && P==-1)break;

    int cnt=0;
    int prime[P];
    for(int i=N+1 ; cnt < P ; i++){
      if(isPrime(i)){
	prime[cnt]=i;
	cnt++;
      }
    }
    int sum[P*P];
    int cnt2=0;
    for(int i=0 ; i < P ; i++){
      for(int j=i ; j < P ; j++){
	sum[cnt2]=prime[i]+prime[j];
	cnt2++;
      }
    }
    sort(sum,sum+cnt2);

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

C++: #include<map>
#include<set>
#include<list>
#include<cmath>
#include<queue>
#include<stack>
#include<cstdio>
#include<string>
#include<vector>
#include<complex>
#include<cstdlib>
#include<cstring>
#include<numeric>
#include<sstream>
#include<iostream>
#include<algorithm>
#include<functional>

#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;

typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;

const int INF=1<<29;
const double EPS=1e-9;

const int dx[]={1,0,-1,0},dy[]={0,-1,0,1};
int n,p;
bool prime[150050];//1000000までの素数を求める
void isprime(){
	for(int i = 0;i <150000;i++){
		prime[i] = true;
	}
	prime[0] = false;
	prime[1] = false;
	for(int i = 2;i*i<150000;i++){
		if(prime[i]){
			for(int j = 2*i;j <150000;j+=i){//素数の倍数は素数ではない
				prime[j]= false;
			}
		}
	}
	return;
}


priority_queue<int, vector<int>, greater<int> > pque;
int main(){
	isprime();
	while(cin>>n>>p){
		if(n==-1&&p==-1){
			break;
		}
		int j = n;
		vector<int> que;
		que.clear();
		while(!pque.empty()){
			pque.pop();
		}
		for(int cnt = 0;cnt <=150;cnt++){
			j++;
			while(!prime[j]){
				j++;
			}
			//cout <<j<<endl;
			que.push_back(j);
		}
		for(int i = 0;i <=150;i++){
			for(int j = i;j <=150;j++){
				int matu =que[i] +que[j];
				pque.push(matu);
			}
		}
		for(int i = 0;i <p-1;i++){
			pque.pop();
		}
		cout<<pque.top()<<endl;
	}
	return 0;
}