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 <cmath>
#include <algorithm>

using std::cin;
using std::cout;
using std::endl;

bool is_prime(int n) {
	if (n < 2) {
			return false;
	}
	if (n==2||n==3) {
		return true;
	}
	for (int i = 3; i < n; i = i+2) {
		if (n%i==0) {
			return false;
		}
	}
	return true;
}

int check_ind(std::vector<int> v, int n) {
	int ind = 0;
	for (std::vector<int>::iterator itr = v.begin(); itr != v.end(); ++itr) {
		if (*itr > n) {
			return ind;
		}
		ind++;
	}
	return 0;
}

int main(void) {
	int n = 101000;
	std::vector<bool> prime(n);
	std::vector<int> p;
	for (int i = 0; i < n+2; i++) {
		prime[i] = true;
	}
	prime[0] = false;
	prime[1] = false;
	for (int i = 2; i <= sqrt(n); i++) {
		if (is_prime(i)) {
			for (int j = 2; i*j < n+2; j++) {
				prime[i*j] = false;
			}
		}
	}
	for (int i = 2; i < n+2; i++) {
		if (prime[i]) {
			p.push_back(i);
		}
	}

	int N,P;
	cin >> N;
	cin >> P;

	while (N != -1 || P != -1) {
		int ind = check_ind(p, N);
		std::vector<int> sum;

		for (int i = ind; i < ind+(2*sqrt(P))+10; i++) {
			for (int j = i; j < i+(2*sqrt(P))+10; j++) {
				sum.push_back(p[i]+p[j]);
			}
		}

		std::sort(sum.begin(), sum.end());

		cout << sum[P-1] << endl;

		cin >> N;
		cin >> P;
	}

	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <algorithm>
#include <vector>
#include <utility>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <functional>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cassert>
 
using namespace std;
 
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define rep(i,n) REP(i, 0, n)
#define pb push_back
#define mp make_pair
#define all(r) (r).begin(),(r).end()
#define rall(r) (r).rbegin(),(r).rend()
#define fi first
#define se second
 
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;

const int INF = 1e9;
const double EPS = 1e-8;
const int mod = 1e9 + 7;
const ll LINF = 1e18;
const double PI = acos(-1);

struct Input
{
	int n;char c;char str[1024];string s;ll l;
	int nextInt(){scanf("%d", &n);return n;}
	ll nextLong(){scanf("%lld", &l);return l;}
	char nextChar(){scanf("%c", &c);return c;}
	string next(){scanf("%s", str);return string(str);}
	string nextLine(){getline(cin, s);return s;}
};
Input in;

bool isPrime[200000];
vector<int> primes;


int main(){
	rep(i, 200000) isPrime[i] = true;
	isPrime[0] = isPrime[1] = false;
	REP(i, 2, 200000){
		if(!isPrime[i]) continue;
		for(int j = i + i; j < 200000; j += i) isPrime[j] = false;
		primes.pb(i);
	}
	//cout<<primes.size()<<endl;
	while(1){
		int n = in.nextInt(),  p = in.nextInt();
		if(n == -1 && p == -1) break;
		
		vi v;
		int idx = upper_bound(all(primes), n) - primes.begin();
		for(int i = idx; i < primes.size(); i++){
			for(int j = i; j < primes.size(); j++){
				if(v.size() < p + 2) v.pb(primes[i] + primes[j]);
				else{
					sort(all(v));
					if(v.back() > primes[i] + primes[j]){
						v.pop_back();
						v.pb(primes[i] + primes[j]);
					}
					else{
						break;
					}
				}
			}
		}
		
		
		sort(all(v));
		printf("%d\n", v[p-1]);
		
		// rep(i, v.size()) cout<<" "<<v[i];
		// cout<<endl;
	}
}

C++: #include<iostream>
#include<cmath>
#include<algorithm>
using namespace std;
int s[1000], k[10000], n, m, t, p, i, j;
int main() {
	while (true) {
		t = 0; p = 0;
		cin >> n >> m;
		if (n == -1) { break; }
		while (t <= m) {
			if (n < 2) { goto E; }
			for (i = 2; i <= sqrt(n); i++) {
				if (n%i == 0) {
					goto E;
				}
			}
			s[t] = n;
			t++;
		E:;
			n++;
		}
		for (i = 0; i < m; i++) { for (j = i; j < m; j++) { k[p] = s[j] + s[i]; p++; } }
		sort(k, k + p);
		cout << k[m] << endl;
	}
	return 0;
}

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

bool num[1000000];

void prime(){
	num[0] = false;
	num[1] = false;
	for(int i = 2; i < 1000000; i++) num[i] = true;
	for(int i = 2; i < 1000; i++){
		if(!num[i]) continue;
		for(int j = 2*i; j < 1000000; j += i) num[j] = false;
	}
}

int main(){
	prime();
	int n,p;
	while(scanf("%d%d", &n, &p)){
		vector<int> v,vec;
		if(n == -1 && p == -1) break;
		for(int i = n+1; i < 1000000; i++){
			if(num[i]) v.push_back(i);
			if(v.size() == p) break;
		}
		for(int i = 0; i < p; i++){
			for(int j = i; j < p; j++){
				vec.push_back(v[i]+v[j]);
			}
		}
		sort(vec.begin(),vec.end());
		printf("%d\n", vec[p-1]);
	}
}