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>

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;
  }
}

C++: #include <vector>
#include <iostream>
#include <algorithm>
 
using namespace std;
 
bool is_prime(int n, int k = 3)
{
    if(n < k * k) { return true; }
     
    if(n % k == 0) { return false; }
     
    return is_prime(n, k + 2);
}
 
int main()
{
    vector<int> prime = {2};
     
    for(int i = 3; i < 101300; i += 2)
    {
        if(is_prime(i))
        {
            prime.push_back(i);
        }
    }
     
    int n, m;
     
    while(true)
    {
        scanf("%d", &n);
        scanf("%d", &m);
         
        if(n == -1 && m == -1) { break; }
         
        int ptr = distance(prime.begin(), lower_bound(prime.begin(), prime.end(), n + 1));
         
        vector<int> c;
        
        if(m > 7) { m /= 2; }
         
        for(int i = ptr; i < ptr + m; i++)
        {
            for(int j = i; j < ptr + m; j++)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
         
        sort(c.begin(), c.end());
         
        printf("%d\n", c[m - 1]);
    }
     
    return 0;
}

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

int main(){
     bool issosu[101198];
     for(int i= 0; i<= 101197; i++) issosu[i] = true;
     issosu[0] = issosu[1] = false;
     for(int i= 2; i<= 101197; i++){
	  if(issosu[i]){
	       for(int j = i* 2; j <= 101197; j += i){
		    issosu[j] = false;
	       }

	  }
     }
     int N,P;
     while(cin>>N>>P,N!=-1&&P!=-1){
	  vector<int> primes;
	  int p=1;
	  while(primes.size()!=P){
	       if(issosu[N+p])primes.push_back(N+p);
	       ++p;
	  }
	  vector<int> sums;
	  for(int i=0;i<P;i++){
	       for(int j=i;j<P;j++){
		    sums.push_back(primes[i]+primes[j]);
	       }
	  }
	  sort(sums.begin(),sums.end());
	  //unique(sums.begin(),sums.end());
	  cout<<sums[P-1]<<endl;
	  //for(int i=0;i<P;i++)cout<<sums[i]<<endl;
     }
}

C++: #include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int psize = 1000000;
    vector<int>num(psize+1);//prime is 0
    num[0] = num[1] = 1;
    for(int i = 2;i * i <= psize;i++){
        if(num[i])continue;
        for(int j = i * 2;j <= psize;j += i){
            num[j] = 1;
        }
    }
    vector<int>prime;
    rep(i,0,psize+1){
        if(!num[i])prime.push_back(i);
    }
    
    int N,P;
    cin >> N >> P;
    while(N != -1){
        auto itr = upper_bound(prime.begin(), prime.end(), N);
        auto itr2 = itr;
        int d = distance(prime.begin(), itr);
        multiset<int>st;
        /*          
        rep(i,0,100){
            rep(j,0,100){
                st.insert(*itr + *itr2);
                itr2++;
            }
            itr++;
        }
                  */
        rep(i,0,100){
            rep(j,i,100){
                st.insert(prime[i + d] + prime[j + d]);
            }
        }
        //sort(num.begin(), num.end()); 
        //cout << num[P-1] << endl;
        auto itr3 = st.begin();
        rep(i,0,P-1){
            itr3++;
        }
        cout << *itr3 << endl;
        cin >> N >> P;
    }
    
}

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

using namespace std;
#define REP(i,n) for(int i = 0 ; i < n ; ++i)
#define int long long

const int NN = 10000000;

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



int solve(int n)
{
	int p = 0;
	REP(i, n)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;
			}
		}
	}
	return p;
}

signed main(){
	solve(NN);

	while (1){

		vector<int> ar;	
		int a = 0;
		int N, P;
		cin >> N >> P;

		if (N == -1 && P == -1)break;

		REP(i, NN){
			if (prime[a] > N)break;
			a++;
		}

		REP(i, 100){
			for (int j = i; j < 100;++j){
				int x = prime[a + i] + prime[a + j];
				ar.push_back(x);
			}
		}

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

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

	}
	return 0;

}