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 <cstdlib>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <set>
#include <cstring>
#include <cmath>


#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, k, n) for (int i = (int)(k); i < (int)(n); i++)
#define rrep(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define rREP(i, k, n) for (int i = (int)(n) - 1; i >= k; i--)

#define debug(x) cerr <<#x << ": " << x << endl;

#define fi first
#define se second

#define vi vector<int>
#define pb push_back
#define mp make_pair

#define pcnt __builtin_popcount

typedef long long ll;
const ll inf = 900900900100100100;
const int MOD = (int)1e9 + 7;
const double EPS = 1e-9;
const int MID = 255;
using namespace std;


const int MAX_N = 1000000;
int prime[MAX_N + 10];
bool is_prime[MAX_N + 10];
int sieve(int n){
    int p = 0;
    rep(i,n + 1) is_prime[i] = true;
    is_prime[0] = is_prime[1] = false;
    REP(i,2,n + 1){
        if(is_prime[i]) {
            prime[p++] = i;
            for(int j = 2 * i; j <= n; j += i)
                is_prime[j] = false;
        }
    }
    return p;
}

int main(){
    int N,P;
    while(cin >> N >> P,N != -1) {
        int p = sieve(MAX_N);
        int k = 0;
        vector<int> pp;
        rep(i,p){
            if(prime[i] <= N) continue;
            int l = 0;
            REP(j,i,p){
                pp.pb(prime[i] + prime[j]);
                l++;
                if(l > P) break;
            }
            k++;
            if(k > P) break;
        }
        sort(pp.begin(),pp.end());
        // rep(i,P) debug(pp[i]);
        cout << pp[P - 1] << endl;
    }


    return 0;
}

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

using namespace std;

#define NMAX 100

int main(){

	int hurui[20000]={0};
	int prime[10000];
	int table[300000]={0};
	int cnt=0;
	int cou;

	hurui[0]=1,hurui[1]=1;
	for(int i=2;i<20000;i++){
		if(hurui[i]==0){
			prime[cnt]=i;
			cnt++;
			for(int j=i;j<20000;j+=i){
				hurui[j]=1;
			}
		}
	}

	cou=cnt;

	int n,p;

	while(1){
		cin>>n>>p;
		if(n==-1&&p==-1) break;
		cnt=0;
		while(1){
			if(n<prime[cnt]) break;
			cnt++;
		}
		for(int i=0;i<300000;i++) table[i]=0;
		for(int i=cnt;i<cou;i++){
			for(int j=i;j<cou;j++){
				table[prime[i]+prime[j]]++;
			}
		}
		while(p>=0){
			p-=table[cnt];
			cnt++;
		}
		cout<<cnt-1<<endl;
	}
}

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

int main() {
bool a[1300000]={0};
a[1]=1;
for(int i=2;i<650001;i++){
	if(a[i]==1) continue;
	int j=2*i;
	while(j<1300000){
		a[j]=1;
		j=j+i;
	}
}

int b[1400000]={0};
int q=1;
for(int i=0;i<1300000;i++){
	q++;
	while(a[q]==1) q++;	

	 b[i]=q;
	
}
//cout<<b[10]<<endl;
int n,p;
while(cin>>n>>p && n>-1){
	int k=0;
	while(b[k]<=n) k++;
	vector<int> v;
//	cout<<k<<endl;
	for(int ii=k;ii<k+500;ii++){
		for(int j=k;j<=ii;j++){
			v.push_back(b[ii]+b[j]);
	//		cout<<ii<<" "<<j<<endl;
			}	
	}
sort(v.begin(),v.end());
//for(int i=0;i<40;i++) cout<<v[i]<<endl;
	cout<<v[p-1]<<endl;
	
}



	return 0;
}

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++: // 2016-12-12
#include <iostream>
#include <algorithm>
#include <cmath>
#include <array>
#include <map>
#include <vector>
using namespace std;

int main() {
	int n, p;
	bool a[100275];
	fill(a, a + 100275, true);
	a[0] = a[1] = false;
	vector<int> v;
	for (int i = 2; i < 100275; i++) {
		if (a[i]) {
			v.push_back(i);
			for (int j = i + i; j < 100275; j += i) {
				a[j] = false;
			}
		}
	}
	vector<pair<int, int>> w;
	for (int i = 0; i < v.size(); i++) {
		for (int j = i, l = min((int)v.size(), i + 20); j < l; j++) {
			if (v[i] + v[j] > 200274) {
				break;
			} else {
				w.push_back(make_pair(v[i] + v[j], min(v[i], v[j])));
			}
		}
	}
	sort(begin(w), end(w));
	while (cin >> n >> p, n >= 0) {
		int i, m;
		for (i = 0, m = 0; i < w.size(); i++) {
			if (w[i].second > n) {
				m++;
				if (m >= p) {
					break;
				}
			}
		}
		cout << w[i].first << endl;
	}
	return 0;
}