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 <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <cstring>
#include <string>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <ctime>
using namespace std;
typedef long long int ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define RREP(i,x) for(int i=(x)-1;i>=0;i--)
#define RFOR(i,c) for(auto i=(c).rbegin();i!=(c).rend();++i)
#define ALL(container) container.begin(), container.end()
#define SZ(container) ((int)container.size())

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;

vi eratosthenes_sieve(int n){
	vi res(n+1);
	if(n<2) return res;
	res[2]=1;
	for(int i=3;i<=n;i+=2){
		if(i*i<=n && !res[i]) for(int j=i+i+i;j<=n;j+=i+i) res[j]=1;
		res[i]=!res[i];
	}
	return res;
}
vi prime_list(const vi& isprime){
	vi res;if(isprime.size()<=2)return res;
	res.push_back(2);
	for(unsigned int i=3;i<isprime.size();i+=2)
		if(isprime[i])res.push_back(i);
	return res;
}
vi prime_list(int n){
	return prime_list(eratosthenes_sieve(n));
}

int n, p;
main(){
	vi pl = prime_list(200000);
	while(cin >> n >> p, n >= 0){
		auto it = upper_bound(ALL(pl), n);
		vi l;
		REP(i, p)REP(j, i+1) l.push_back(*(it+i) + *(it+j));
		sort(ALL(l));
		cout << l[p-1] << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
using namespace std;
	bool is(int x){
		for(int i=2;i*i<=x;i++)if(x%i==0)return false;
		return true;
	}
int main(){
	int n,p;

	while(cin>>n>>p,n!=-1||p!=-1){
		int cnt=0;
		n++;
		if(n==1)n++;
		vector<int>primes;
		vector<int>sums;
		while(true){
			if(is(n)){
				cnt++;
				primes.push_back(n);
			}
			if(cnt==20)break;
			n++;
		}
		//for(int i=0;i<primes.size();i++)cout<<primes[i]<<endl;
		for(int i=0;i<primes.size();i++){
			for(int j=0;j<primes.size();j++){
				if(j>primes.size())break;
				if(i<j)break;
				sums.push_back(primes[i]+primes[j]);
			}
		}
		sort(sums.begin(),sums.end());
		cout<<sums[p-1]<<endl;
	}
	return 0;
}

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[50];
        priority_queue<ll, vector<ll>, greater<ll> > pq;
        
        int idx = n;

        for (int i = 0; i < 30; i++) {
            while (!prime[++idx])
                ;
            pr[i] = idx;
        }

        for (int i = 0; i < 30; i++) 
            for (int j = i; j < 30; 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 <bits/stdc++.h>

#define FOR(i, a, b) for(long long int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for(long long int i=(a);i>=(b);i--)
#define MOD 1000000007
#define INF 1000000000 //2000000000
#define LLINF 1000000000000000000 //9000000000000000000
#define PI 3.14159265358979

using namespace std;
typedef long long int ll;
typedef pair< long long int, long long  int> P;



int main(void) {
	int prime[20000] = {};
	int pos = 2;
	prime[1] = 2;
	FOR(i, 3, 200000) {
		bool flag = true;
		FOR(t, 2, sqrt(i) + 1) {
			if (i%t == 0) {
				flag = false;
				break;
			}
		}
		if (flag) {
			prime[pos] = i;
			pos++;
		}
	}
	
	while (1) {
		int n, p;
		int now;
		int count = 0;
		vector<int>dp(210, 0);

		cin >> n >> p;
		if (p == -1) {
			break;
		}
		FOR(i, 1, pos) {
			if (prime[i] > n) {
				now = i;
				break;
			}
		}
		FOR(i, now, now + 19) {
			FOR(t, i, now + 19) {
				dp[count] = prime[i] + prime[t];
				count++;
			}
		}
		/*FOR(i, 0, 209) {
			cout << dp[i] << endl;
		}*/
		sort(dp.begin(), dp.end());
		/*cout << endl;
		FOR(i, 0, 209) {
			cout <<i<<" "<< dp[i] << endl;
		}
		cout << endl;*/
		cout << dp[p - 1] << endl;
	}
	
}