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 <cstdlib>
#include <string>
#include <cmath>
#include <algorithm>
using namespace std;
#define N 100000

int main(){
        int n, p, sosuu[100],count=0,sum[10000];
        string keymoji;

        cin >> n >> p;
        while(n != -1 && p != -1){
                int i=n;
                count = 0;
                int tmp=sqrt(n);
                if(i<2)i=2;
                for(; count<p; i++){
                        int tmp;
                        if(i==2){
                                sosuu[count]=i;
                                count++;
                                continue;
                        }
                        for(int j=2;j<sqrt(i)+1;j++){
                                if((tmp=i%j) == 0)break;
                        }
                        if(tmp != 0){
                                sosuu[count]=i;
                                count++; 
                        }
                        
                }
                count =0;
                for(i=0; i<p; i++){
                        for(int j=i; j<p; j++){
                                sum[count]=sosuu[i]+sosuu[j];
                                count++;
                        }
                }

                sort(sum, sum+count);
                cout << sum[p-1] << endl;
                cin >> n >> p;

        }


}

C++: #include<iomanip>
#include<limits>
#include<thread>
#include<utility>
#include<iostream>
#include<string>
#include<algorithm>
#include<set>
#include<map>
#include<vector>
#include<stack>
#include<queue>
#include<cmath>
#include<numeric>
#include<cassert>
#include<random>
#include<chrono>
#include<unordered_set>
#include<unordered_map>
#include<fstream>
#include<list>
#include<functional>
#include<bitset>
#include<complex>
#include<tuple>
using namespace std;
typedef unsigned long long int ull;
typedef long long int ll;
typedef pair<ll,ll> pll;
typedef long double D;
typedef complex<D> P;
#define F first
#define S second
const ll E=1e18+7;
const ll MOD=1000000007;


template<typename T,typename U>istream & operator >> (istream &i,pair<T,U> &A){i>>A.F>>A.S; return i;}
template<typename T>istream & operator >> (istream &i,vector<T> &A){for(auto &I:A){i>>I;} return i;}
template<typename T,typename U>ostream & operator << (ostream &o,pair<T,U> &A){o<<A.F<<" "<<A.S; return o;}
template<typename T>ostream & operator << (ostream &o,vector<T> &A){ll i=A.size(); for(auto &I:A){o<<I<<(--i?" ":"");} return o;}
template<typename T>vector<T> & cset(vector<T> &A,T e=T()){for(auto &I:A){I=e;} return A;}



int main(){
    const ll MAX=1000000;
    vector<bool> P(MAX,true);
    for(ll i=2;i<MAX;i++){
        if(P[i]){
            for(ll j=2;i*j<MAX;j++){P[i*j]=false;}
        }
    }
    ll n,p;
    while(cin>>n>>p,n!=-1){
        vector<ll> A;
        for(ll i=max(2LL,n+1);A.size()<p+100;i++){
            if(P[i]){
                A.push_back(i);
            }
        }
        vector<ll> B;
        for(int i=0;i<A.size();i++){
            for(int j=i;j<A.size();j++){
                B.push_back(A[i]+A[j]);
            }
        }
        sort(B.begin(),B.end());
        cout<<B[p-1]<<endl;
    }
    
    
    
    return 0;
}

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

typedef long long LL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define DECIM8  fixed<<setprecision(8) 
#define SZ(a) int((a).size())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

using namespace std;
int main(void)
{
  bool prime[262144];
  REP(i,262144) prime[i]=true;
  prime[0]=false;prime[1]=false;
  REP(i,sqrt(262144)) if(prime[i]) for(int j=i*i;j<262144;j+=i) prime[j]=false;
  vector<int> primev;
  REP(i,262144) if(prime[i]) primev.PB(i);
  for(;;){
    int n,p;
    cin >> n >> p;
    if(n==-1&&p==-1) return 0;
    vector<int> lp;
    vector<int> mnp;
    int i=0;
    while(primev[i]<=n) ++i;
    REP(j,100) lp.PB(primev[i+j]);
    for(auto x:lp) for(auto y:lp) if(x<=y) mnp.PB(x+y);
    SORT(mnp);
    cout << mnp[p-1] << endl;
  }
}