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<stdio.h>
#include<iostream>
#include<string>
#include<algorithm>
#include <vector>
#include<math.h>


using namespace std;

bool f[1000002];

int main(){
	for(int i=3;i<1000001;i+=2){f[i]=true;
		for(int j=3;j*j<=i;j+=2)
			if(i%j==0)f[i]=false;
	}
	f[2]=true;
	int n,p;
	while(1){
		cin>>n>>p;if(n==-1&&n==p)break;

		int r=0;
		int q[10001]={};
		int x=0;
		int y=n;
		while(1){
			if(f[y]==true)x++;
			if(x==p)break;
			y++;
		}
		n++;
		 vector<int> anslist;
		 for(int i=n;i<=y;i++)
			for(int j=i;j<=y;j++)
			{
				if(f[i]==true&&f[j]==true){
					anslist.push_back(i+j);
				
				//cout<<i<<" "<<j<<endl;
				}
			}
			sort(anslist.begin(),anslist.end());
/*
		for(int i=n;i<=y;i++)
			for(int j=i;j<=y;j++)
			{
				if(f[i]==true&&f[j]==true){
				q[r]=i+j;r++;
				}
			}

		/*	
		sort(q,q+r);
		for(int i=0;i<r;i++)
		cout<<q[i]<<endl;

		cout<<q[p-1]<<endl;*/
			  cout << anslist[p-1] << endl;

	}
	
	return 0;
}

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

//define
#define ALL(a) a.begin(),a.end()
#define REP(i,n) for(int i=0;i<n;i++)
#define RREP(i,n) for(int i=n-1;i>=0;i--)
#define debug(x) if(1) cout<<#x<<":"<<x<<endl;
#define DEBUG(x) if(1) cout<<#x<<":"<<x<<endl;
#define ll long long

//constant
const int MOD=1000000007;
const int INF=INT_MAX/3-1;
const double EPS=1e-9;
const int dx[]={1,0,-1,0};
const int dy[]={0,1,0,-1};

//typedef
typedef vector<int> vi;
typedef vector<vector<int>> vvi;


bool isnprime[1000000];

int main(){
    isnprime[0]=1;
    isnprime[1]=1;
    for(int i=2;i<1000000;i++)
        if(!isnprime[i])
            for(int j=i*2;j<1000000;j+=i)
                isnprime[j]=1;
    int n,p;
    while(cin>>n>>p,n!=-1){
        vi prime(p);
        int count=0;
        for(int i=n+1;i<1000000 && count<p;i++)
            if(!isnprime[i]){
                prime[count]=i;
                count++;
            }

        vi sum(p*(p+1)/2);
        count=0;
        REP(i,p)
            for(int j=i;j<p;j++)
                sum[count]=prime[i]+prime[j],count++;
        sort(ALL(sum));
        cout<<sum[p-1]<<endl;


    }


return 0;
}

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

#define MEMZERO(x) memset(x, 0, sizeof(x))
#define MEMSET(x, y) memset(x, y, sizeof(x))

using namespace std;

const int SIZE = 101200;
bool isPrime[SIZE];
int prime[SIZE/2], pSize;
int table[5100];

void setPrime( void )
{
	pSize = 0;
	for(int i=2; i < SIZE; ++i) isPrime[i] = true;
	isPrime[0] = isPrime[1] = false;
	for(int i=2; i < SIZE; ++i) {
		if(!isPrime[i]) continue;
		prime[pSize++] = i;
		for(int j=i+i; j < SIZE; j+=i) {
			isPrime[j] = false;
		}
	}
}

int search_index( int num )
{
	int l=0, h = pSize;
	while(l < h) {
		int m = (l + h) / 2;
		if(prime[m] < num) l = m + 1;
		else if(prime[m] > num) h = m;
		else return (m+1);
	}
	return l;
}

int main( void )
{
	setPrime();
	int m, p;
	while(cin >> m >> p, m != -1 || p != -1) {
		MEMZERO(table);
		int ii = search_index(m);
		int count = 0;
		for(int i=0; i < 100; ++i)
			for(int j=i; j < 100; ++j) {
				table[count++] = prime[i+ii] + prime[j+ii];
			}
		sort(table, table+count);
		cout << table[p-1] << endl;
	}
	return 0;
}

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

using namespace std;

#define MAX 1000001

vector<int> vprimes;
bool *isPrime = new bool[MAX];

/* ツ素ツ青板青カツ青ャ O(n^2) */
void MakePrime(){
  isPrime[0]=false;
  isPrime[1]=false;
  isPrime[2]=true;
  for(int i = 2; i < MAX; ++i){
    isPrime[i] = true;
  }
  for(long long int i = 2; i < MAX; ++i){
    if( isPrime[i] ){
      for(long long int j = 2; i * j < MAX; ++j) {
	isPrime[i*j] = false;
      }
    }
  }
  for(int i = 0; i < MAX; ++i){
    if( isPrime[i] ){
      vprimes.push_back( i );
    }
  }
}

int main()
{
  MakePrime();
  int N,P;
  while(cin>>N>>P&&(N>=0)&&(P>=0)){
    vector<int> v;
    vector<int> primes;
    for(int i = 0; i < vprimes.size(); ++i){
      if(vprimes[i]>N)primes.push_back(vprimes[i]);
    }
    for(int i = 0; i < primes.size(); ++i){
      for(int j = i; j < primes.size(); ++j){
	v.push_back(primes[i]+primes[j]);
	if(v.size()>MAX)break;
      }
    }
    nth_element(v.begin(),v.begin()+P,v.end());
    cout << v[P-1] << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
bool is_prime(int n){
	for(int i=2;i*i<=n;i++){
		if(n%i==0)return false;
	}
	return n!=1;
}
int main(){
	int n,p;
	while(1){
		cin>>n>>p;
		if(n==-1&&p==-1)break;
		vector<int> prime,sum;
		int cnt=0;
		while(cnt<p){
			n++;
			if(is_prime(n)){
				prime.push_back(n);
				cnt++;
			}
		}
		for(int i=0;i<prime.size();i++){
			for(int j=i;j<prime.size();j++){
				sum.push_back(prime[i]+prime[j]);
			}
		}
		sort(sum.begin(),sum.end());
		cout<<sum[p-1]<<endl;
	}
}