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 <bits/stdc++.h>

#define loop(n, i) for(int i=0;i<n;i++)
#define all(v) v.begin(),v.end()
#define HERE cout << "HERE: " << __LINE__ << endl;
#define INSP(v) cout << v << " at " << __LINE__ << endl;

using namespace std;
typedef long long ll;


int main()
{
    int max = 110000;
    vector<int> mat(max, 1);
    vector<int> primes;
    for (int i=2; i<sqrt(max); i++) {
        if (mat[i]) {
            for (int j=i*2; j < max; j+=i) mat[j] = 0;
        }
    }
    for (int i=2; i<max; i++) {
        if (mat[i]) primes.push_back(i);
    }

     // for (auto n:primes) cout << n << endl;

    int n, p;
    while (cin >> n >> p) {
        if (n == -1) break;

        int start;
        for (int i = 0; i < primes.size(); i++) {
            if (n < primes[i]) {
                start = i;
                break;
            }
        }

        vector<int> nums;
        for (int i = start; i < start+100; i++) {
            for (int j = i; j < start+100; j++) {
                nums.push_back(primes[i]+primes[j]);
                //cout << primes[i] << '+' << primes[j] << '=' << primes[i]+primes[j] <<  endl;
            }
        }

        sort(all(nums));
//        cout << "sorted nums!---------" << endl;
//        for (auto n:nums) cout << n << endl;
//        cout << "sorted nums!---------" << endl;
        //loop(100,i) INSP(nums[i])
        cout << nums[p-1] << endl;

    }
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <vector>
#include <deque>
#include <list>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <cstring>
#include <cctype>
#include <sstream>
#include <set>
#include <map>
#include <queue>
#include <complex>
using namespace std;
#define REP(i,n) for(int i = 0; i < (int)n; i++)
#define FOR(i,a,b) for(int i = a; i < (int)b; i++)
const int INF = 1<<28;

bool prime[200 * 1000] = {};
void pre() {
	memset(prime, true, sizeof(prime));
	prime[0] = prime[1] = false;
	REP(i, 200 * 1000)
		if(prime[i])
			for(int j = i*2; j < 200 * 1000; j += i)
				prime[j] = false;
	return;
}

int main() {
	pre();
	int N, P;
	while(cin >> N >> P) {
		if(N == -1 && P == -1) break;
		vector<int> line;
		int cnt = 0;
		for(int i = N+1;; i++) {
			if(prime[i]) {
				line.push_back(i);
				cnt++;
			}
			if(cnt == (int)sqrt(P)*2) break;
		}
		vector<int> ans;
		REP(i, line.size())
			FOR(j, i, line.size())
				ans.push_back(line[i] + line[j]);
		sort(ans.begin(), ans.end());
//		REP(i, ans.size()) cout << ans[i] << ", ";
		cout << ans[P-1] << endl; 
	}
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define INF 1000000000

int main(void){
    
    vector<bool> array(1000000, true);
    array[0] = array[1] = false;
    for(int i = 2; i < 1000000; i++){
        if(array[i] == true){
            for(int j = 2*i; j < 1000000; j += i) array[j] = false; 
        }
    }

    vector<int> so;
    for(int i = 0; i < 1000000; i++){
        if(array[i] == true) so.push_back(i);
    }

    /*for(int i = 0; i < 10; i++){
        cout << so[i] << " ";
    }
    cout << endl;*/


    //  ?????????????§???????
    int N, P;
    while(1){
        cin >> N >> P;
        if(N == -1) break;
        int start = 0;
        while(1){
            if(so[start] > N) break;
            start++;
        }
        //cout << start << endl;
        //cout << 37 << endl;
        vector<int> sum;
        for(int i = start; i < start + P; i++){
            for(int j = start; j <= i; j++){
                sum.push_back(so[i] + so[j]);
            }
        }
        //cout << 44 << endl;
        sort(sum.begin(), sum.end());
        //cout << endl;
        //cout << 50 << endl;
        cout << sum[P - 1] << endl;
    }
    
    return 0;
}

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

using namespace std;

const int K=150000;
bool A[K];
vector<int> prime;
void F(){
   for(int i=0; i<K; i++) A[i]=true;

   A[0]=A[1]=false;
   for(int i=0; i*i<=K; i++){
      if(A[i])for(int j=2; (i*j)<K; j++){
         A[i*j]=false;
      }
   }
   for(int i=0; i<K; i++){
      if(A[i]) prime.push_back(i);
   }
}

signed main(){

   F();
   while(1){
      int N, P;
      cin>> N>> P;
      if(N==-1&&P==-1) break;

      N++;
      vector<int> v;
      while(A[N]==false) N++;
      int hoge=0;
      for(int i=0; i<prime.size(); i++){
         if(prime[i]==N){hoge=i;break;}
      }
      for(int i=hoge; i<=hoge+P; i++){
         for(int j=0; j<P; j++){
            v.push_back(prime[i]+prime[i+j]);
         }
      }
      sort(v.begin(), v.end());

      cout<< v[P-1]<< endl;
   }

   return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
vector<ll> prime;
ll size = 1010101;
int main() {
  vector<bool> used(size);
  for (int i = 2; i < size; i++) {
    if (!used[i]) {
      prime.push_back(i);
      for (int j = 1; i * j < size; j++)
        used[i * j] = true;
    }
  }
  while (true) {
    int n, p;
    cin >> n >> p;
    if (n == -1)
      break;
    auto it = upper_bound(prime.begin(), prime.end(), n);
    vector<ll> ps;
    for (int i = 0; i < p; i++)
      for (int j = i; j < p; j++)
        ps.push_back((*(it + i)) + (*(it + j)));
    sort(ps.begin(), ps.end());
    cout << ps[p - 1] << endl;
  }
  return 0;
}