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 <queue>

using namespace std;

typedef long long ll;

const int prime_max = 100500;
bool prime[prime_max + 1];

void initial_prime()
{
    for (int i = 0; i < prime_max; i++)
        prime[i] = true;

    prime[0] = prime[1] = false;
    for (int i = 2; i * i < prime_max; i++) {
        if (prime[i])
            for (int j = 2 * i; j < prime_max; j += i)
                prime[j] = false;
    }
}


int main()
{
    int p;
    ll n;

    initial_prime();
    
    while (cin >> n >> p, n != -1 || p != -1) {
        ll pr[25];
        priority_queue<ll, vector<ll>, greater<ll> > pq;
        
        int idx = n;

        for (int i = 0; i < 20; i++) {
            while (!prime[++idx])
                ;
            pr[i] = idx;
        }

        for (int i = 0; i < 20; i++) 
            for (int j = i; j < 20; j++) 
                pq.push(pr[i] + pr[j]);

        for (int i = 0; i < p - 1; i++)
            pq.pop();
        cout << pq.top() << endl;
    }

    return 0;
}

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];
vi v;

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;
    }
  }
  //rep(i,50)cout<<"DEBUG "<<prime[i]<<endl;
}

void solve(int n,int p){
  v.clear();
  int x=0;
  while(prime[x]<=n){
    //cout<<x<<" "<<prime[x]<<endl;
    x++;
  }
  
  REP(i,x,x+p){
    REP(j,i,x+p){
      v.push_back(prime[i]+prime[j]);
    }
  }
  sort(all(v));
  //rep(i,p)cout<<i+1<<" "<<v[i]<<endl;
  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 <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[150000];
bool is_prime[150000];
vector<ll> v;

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;
    }
  }
  //rep(i,50)cout<<"DEBUG "<<prime[i]<<endl;
}

void solve(int n,int p){
  ll data[11000];
  int x=0;
  while(prime[x]<=n){
    //cout<<x<<" "<<prime[x]<<endl;
    x++;
  }
  int cnt=0;
  REP(i,x,x+p){
    REP(j,i,x+p){
      data[cnt]=(prime[i]+prime[j]);
      cnt++;
    }
  }
  sort(data,data+cnt);
  //rep(i,p)cout<<i+1<<" "<<v[i]<<endl;
  cout<<data[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 <iostream>
#define N 200000
using namespace std;
int main(){
  int n,p,sosu[N],i,j,result,data[N],l,flag,temp;
  for(i=0;i<N;i++) sosu[i]=1;
  sosu[0]=0;
  sosu[1]=0;
  for(i=2;i<N/2;i++){
    if(sosu[i]==1){
      for(j=i*2;j<N;j+=i){
        sosu[j]=0;
      }
    }
  }
  while(1){
    flag=0;
    l=0;
    cin >> n >> p;
    if(n==-1&&p==-1) break;
    for(i=n+1;i<N;i++){
      if(sosu[i]==1){
	for(j=n+1;j<=i;j++){
          if(sosu[j]==1){
            data[l]=i+j;
	    l++;
	    if(l==p+100){
	      flag=1;
	      break;
	    }
	  }
	}
	if(flag==1) break;
      }
    }
    for(i=1;i<p+100;i++){
      for(j=1;j<p+100;j++){
	if(data[j]<=data[j-1]){
	  temp=data[j];
	  data[j]=data[j-1];
	  data[j-1]=temp;
	}
      }
    }
    cout << data[p-1] << endl;
  }
  return 0;
}