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 <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 = idx; j < primes.size(); j++){
				v.pb(primes[i] + primes[j]);
			}
		}
		
		sort(all(v));
		printf("%d\n", v[p]);
	}
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef complex<double> Point;

#define PI acos(-1.0)
#define EPS 1e-10
const ll INF = 1e16;
const ll MOD = 1e9 + 7;

#define FOR(i,a,b) for(ll i=(a);i<(b);i++)
#define rep(i,N) for(ll i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define EQ(a,b) (abs((a)-(b))<EPS)
#define EQV(a,b) ( EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()) )
#define fi first
#define se second
#define N_SIZE (1LL << 20)
#define NIL -1

ll mod_add(ll a, ll b) { return (a + b) % MOD; }
ll mod_sub(ll a, ll b) { return (a - b + MOD) % MOD; }
ll mod_mul(ll a, ll b) { return a*b % MOD; }

int n,p;
bool is_prime[200100];
vector<ll> prime;

void sieve(){
    rep(i,200000)is_prime[i] = 1;
    is_prime[0] = is_prime[1] = 0;
    for(ll i = 2;i <= 200000;i++){
        if(is_prime[i]){
            prime.push_back(i);
            for(ll j = 2*i;j <= 200000;j += i)is_prime[j] = 0;
        }
    }
}

int main(){
    sieve();
    while(cin >> n >> p && n != -1){
        auto it = upper_bound(ALL(prime),n);
        ll b = it - prime.begin();
        vector<ll> ans;
        for(int i = 0;i <= 100;i++){
            for(int j = i;j <= 100;j++){
                ans.push_back(prime[i+b]+prime[j+b]);
            }
        }   
        sort(ALL(ans));
        // rep(i,p){
        //     cout << ans[i] << " ";
        // }
        // cout << endl;
        cout << ans[p-1] << endl;
    }

}

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

bool check(int x){
	if(x == 2)return true;
	if(x == 1 || x%2 == 0)return false;
	for(int i = 3;i <= sqrt(x);i+=2){
		if(x%i == 0)return false;
	}
	return true;
}

int main(){
	int n,p;
	vector<int> v,res;
	while(1){
		cin >> n >> p;
		if(n < 0)break;
		v.clear();
		res.clear();
		for(int i = n+1;;i++){
			if(check(i))v.push_back(i);
			if(v.size() > 1000)break;
		}
		//for(int i = 0;i < 100;i++){
		//	cout << v[i] << endl;
		//}
		for(int i = 0;i < 1000;i++){
			for(int j = i;j < 1000;j++){
				res.push_back(v[i] + v[j]);
			}
		}
		sort(res.begin(),res.end());
		cout << res[p-1] << endl;

	}
	return 0;
}

C++: #include<iostream>
#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) {
			n++;
			if (n < 2) { goto E; }
			for (i = 2; i*i <= n; i++) {
				if (n%i == 0) {
					goto E;
				}
			}
			s[t] = n;
			t++;
		E:;
		}
		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 - 1] << endl;
	}
	return 0;
}