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 <numeric>
#include <climits>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <queue>
#include <vector>
#include <algorithm> 
#include <math.h>
/*
   メモ
#inlucde <string>
memset(配列,初期化値,sizeof(配列));//配列初期化

#include <queue>
push(),back(),front()
pop()//最初の要素削除

#inclue <stack>
pop(),push(),top(),empty()

__builtin_popcount(unsigned int);

*/

#define ALL(v) (v).begin(),(v).end()
#define REP(i,p,n) for(int i=p;i<(int)(n);++i)
#define rep(i,n) REP(i,0,n)
#define dump(a) (cerr << #a << "=" << (a) << endl)
#define DUMP(list) cout << "{"; for(auto nth : list){ cout << nth << " ";}cout << "}" << endl;

using namespace std;
const int SIZE= 1000000;
bool prime[SIZE];
vector<int> primes;

int main() {
	rep (i, SIZE) prime[i] = true;
	prime[0] = prime[1] = false;
	//素数生成
	for (int i = 0; i * i <= SIZE; ++i) {
		if (!prime[i]) continue;
		for (int j = i * i; j <= SIZE; j += i) {
			prime[j] = false;
		}
	}
	rep (i, SIZE) if (prime[i]) primes.push_back(i);
	
	

	int n, p;
	while (true) {
		cin >> n >> p;
		if (n == -1 && p == -1) break;
		
		//イテレータから要素取り出し
		int pos = upper_bound(primes.begin(), primes.end(), n) - primes.begin();
		

		vector<int> res;
		rep (i, p) rep (j, p) {
			res.push_back(primes[pos + i] + primes[pos + i + j]);
		}
		sort(res.begin(), res.end());
		cout << res[p - 1] << endl;

	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
long long int flag[200000] = {0};

int main() {

  long long int cnt = 1;

  vector< long long int > sosu;

  for ( long long int i = 2; i < 200000; i++ ) {

    if ( flag[i] == 0 ) {
      sosu.push_back( i );
      flag[i] = cnt;
      cnt++;
      for ( long long int j = 2; j * i < 200000; j++ ) {
	flag[j*i] = -1;
      }
    }

  }

  long long int n, p;

  while( true ) {

    cin >> n >> p;

    if ( n == -1 ) break;

    cnt = 1;

    while( true ) {
      if ( flag[n+cnt] > 0 ) {
	cnt = flag[n+cnt] - 1;
	break;
      }
      cnt++;
    }

    vector< long long int > ans;

    for ( long long int i = 0; i < p; i++ ) {
      for ( long long int j = i; j < p; j++ ) {
	ans.push_back( sosu[ cnt+i ] + sosu[ cnt+j ] );
      }
    }
    sort( ans.begin(), ans.end() );

    cout << ans[p-1] << endl;

  }

  return 0;

}

C++: #include <bits/stdc++.h>
using namespace std;
const int MAX = 1e6;
bool prime[MAX];
signed
main(){
	vector<int> pnum;
	for(int i=0;i<MAX;i++)
		prime[i] = true;
	prime[1] = false;
	for(int i=2;i<MAX;i++)
	{
		if(prime[i])
		{
			pnum.push_back(i);
			for(int j=2*i;j<MAX;j+=i)
				prime[j] = false;
		}
	}

	int n,p;
	while(cin >> n >> p)
	{
		if(n==-1 and p==-1) break;
		int cnt = 0;
		while(1)
		{
			if(pnum[cnt]>n) break;
			else cnt++;
		}
		vector<int> ans;
		for(int i=cnt;i<cnt+p;i++)
		{
			for(int j=i;j<cnt+p;j++)
			{
				ans.push_back(pnum[i]+pnum[j]);
			}
		}
		sort(ans.begin(),ans.end());
		cout << ans[p-1] << endl;
	}
}

C++: #include "bits/stdc++.h"

#define REP(i,n) for(ll i=0;i<n;++i)
#define RREP(i,n) for(ll i=n-1;i>=0;--i)
#define FOR(i,m,n) for(ll i=m;i<n;++i)
#define RFOR(i,m,n) for(ll i=n-1;i>=m;--i)
#define ALL(v) (v).begin(),(v).end()
#define PB(a) push_back(a)
#define UNIQUE(v) v.erase(unique(ALL(v),v.end()));
#define DUMP(v) REP(i, (v).size()) { cout << v[i]; if (i != v.size() - 1)cout << " "; else cout << endl; }
#define INF 1000000001ll
#define MOD 1000000007ll
#define EPS 1e-9

const int dx[8] = { 1,1,0,-1,-1,-1,0,1 };
const int dy[8] = { 0,1,1,1,0,-1,-1,-1 };


using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
///(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)///
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	vl prime = { 2 };
	FOR(i, 3,150000) {
		int flag = 1;
		REP(j, prime.size()) {
			if (i%prime[j] == 0)flag = 0;
		}
		if (flag)prime.push_back(i);
	}

	int n, p;
	while (1) {
		cin >> n >> p;
		if (n == -1)break;
		int c = lower_bound(ALL(prime), n) - prime.begin();
		vl v(p*p);
		REP(i, p) {
			REP(j, p) {
				v[i*p + j] = prime[i] + prime[j];
			}
		}
		sort(ALL(v));
		cout << v[p - 1] << endl;
	}
	return 0;
}