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 <bits/stdc++.h>
using namespace std;

vector<int> prime;

void hurui(){
  prime.push_back(2);
  for(int i=3;i<=1000000;i++){
    int flag=1;
    for(int j=0;j<prime.size()&&prime[j]*prime[j]<=i;j++){
      if(i%prime[j]==0){
	flag=0;
	break;
      }
    }
    if(flag==1)prime.push_back(i);
  }
}
	
      
int n,p;
vector<int> np;
vector<int> nppl;
int main(){
  hurui();
  while(1){
    cin>>n>>p;
    np.clear();
    while(nppl.size())nppl.pop_back();
    if(n==-1&&p==-1)break;
    for(int i=0;i<prime.size()&&np.size()<=120;i++){
      if(prime[i]>n){
	np.push_back(prime[i]);
      }
    }
    for(int i=0;i<np.size();i++){
      for(int j=i;j<np.size();j++){
	nppl.push_back(np[i]+np[j]);
      }
    }
    sort(nppl.begin(),nppl.end());
    cout<<nppl[p-1]<<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <functional>
#include <cstdlib>
#include <sstream>
#include <string>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <complex>
#include <vector>
#include <bitset>
#include <cstdio>
#include <cmath>
#include <time.h>
#include <tuple>
#define all(c) ((c).begin(),(c).end())
#define rall(c) ((c).rbegin(),(c).rend())
//#define sort(v,n) sort(v,v+n)
#define ll long long
#define fi first
#define se second
#define inf 999999999
using namespace std;
const ll MOD = 1e9 + 7;
const double PI = acos(-1.0);
//---------------------------------------------------------------------------------------------//
bool a[300000];
inline void sosuu() {
	for (int i = 0; i < 300000; i++) {
		a[i] = 1;
	}
	int now = 2;
	while (now<=150000) {
		if (a[now]) {
			for (int i = now * 2; i < 300000; i += now) {
				a[i] = 0;
			}
		}
		now++;
	}
	a[0] = 0;
	a[1] = 0;
}


int main() {
	sosuu();
	int n, p;
	while (cin >> n >> p) {
		if (n == -1)return 0;
		int cont = 0;
		bool flag = 0;
		vector<int> v;
		for (int i = n+1;i<300000; i++) {
			for (int j = n+1;j<=i; j++) {
				if (a[i] && a[j]) {
					cont++;
					v.push_back(i + j);
				}
				else {
					continue;
				}
				if (cont == p+100) {
					flag = 1;
					break;
				}
			}
			if (flag)break;
		}
		sort(v.begin(), v.end());
		//for (int i = 0; i < v.size(); i++)cout << "v" << v[i] << endl;
		cout << v[p - 1] << endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;

const int MAX_N = 1000000;

int prime[MAX_N];
bool is_prime[MAX_N + 1];

void eratos(int n) {
    int p = 0;
    for (int i = 0; i <= n; ++i) is_prime[i] = true;
    is_prime[0] = is_prime[1] = false;
    for (int i = 2; i <= n; ++i) {
        if (is_prime[i]) {
            prime[p++] = i;
            for (int j = 2*i; j <= n; j += i) is_prime[j] = false;
        }
    }
}

int main() {
    eratos(MAX_N);

    int N, P;

    while (cin >> N >> P, (N != -1 and P != -1)) {
        vector<int> t(100);
        int cnt = 0;

        for (int i=N+1; i<MAX_N; ++i) {
            if (is_prime[i]) { t[cnt++] = i; }
            if (cnt >= 100) break;
        }

        vector<int> tt(1000);
        cnt=0;
        rep(i, 100) {
            for (int j=i; j<100; ++j) {
                tt[cnt++] = t[i] + t[j];
            }
        }

        sort(tt.begin(), tt.end());

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

    }

}