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 endl '\n';
#define rep(i,n) for(int i=0; i<(n); i++)
using namespace std;
using ll = long long;
using P = pair<int,int>;
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast")
constexpr ll INF = 1e18;
constexpr int inf = 1e9;
constexpr double INFD = 1e100;
constexpr ll mod = 1000000007;
constexpr ll mod2 = 998244353;
const double PI = 3.1415926535897932384626433832795028841971;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
// ios::sync_with_stdio(false);
// cin.tie(nullptr);
// ---------------------------------------------------------------------------


int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    vector<int> eratosthenes(10'000'000,0);
    eratosthenes[0] = eratosthenes[1] = 1;
    for(int i=2; i<10'000'000; i++){
        if(eratosthenes[i]==0){
            for(int j=i+i; j<10'000'000; j+=i){
                eratosthenes[j] = 1;
            }
        }
    }
    vector<int> sosu;
    for(int i=0; i<10'000'000; i++){
        if(eratosthenes[i] == 0) sosu.push_back(i);
    }
    int N,p;
    cin >> N >> p;
    while(N != -1){
        int pos = upper_bound(sosu.begin(),sosu.end(),N) - sosu.begin();
        vector<int> vec;
        for(int i=0; i<p; i++){
            for(int j=i; j<p; j++){
                vec.push_back(sosu[pos+i]+sosu[pos+j]);
            }
        }
        sort(vec.begin(),vec.end());
        cout << vec[p-1] << endl;
        cin >> N >> p;
    }
    return 0;
}

C++: #include<iostream>
#include<vector>
#include<string>
#include<algorithm>
using namespace std;
int main(){
  int n,p;
  while(cin >> n >> p){
    if(n==-1)break;
    int m,sosu[200]={},count=0,judge=1;
    for(m=n+1;count<=200;m++){
      for(int i=2;i<m;i++){
        if(m%i==0){
          judge=0;
        }
      }
      if(judge==1&&m!=1){
        sosu[count]=m;
        count++;
      }
      else judge=1;
    }
    vector<int> sum(200);
    int COUNT=0;
    for(int i=0;i<10;i++){
      for(int j=i;j<25;j++){
        sum[COUNT]=sosu[i]+sosu[j];
        COUNT++;
      if(COUNT==200)break;
      }
      if(COUNT==200)break;
    }
    sort(sum.begin(),sum.end());
    cout << sum[p-1] << endl;
  }
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
typedef vector<int> vi;
#define loop(i,a,b) for(int i=(a); i<int(b); i++)
#define rep(i,b) loop(i,0,b)
#define all(c) (c).begin(), (c).end()

int const N = 100000+10000;
bool isp[N];
int ps[N / 2];
int c = 0;
void eratos(){
    rep(i, N) isp[i] = true;
    isp[0] = isp[1] = false;
    for (int i = 2; i < N; i++){
        if (!isp[i]) continue;
        ps[c++] = i;
        for (int j = i + i; j < N; j += i){
            isp[j] = false;
        }
    }
}

int solve(int n, int p){
    auto it = upper_bound(ps, ps + c, n);
    vi v(p*p, 1 << 30);
    rep(i, p)loop(j, i, p){
        v[i * p + j] = *(it + i) + *(it + j);
    }
    v.erase(lower_bound(all(v), 1 << 30), v.end());
    sort(all(v));
    return v[p - 1];
}

int main(){
    eratos();
    int n, p;
    while (cin >> n >> p && n!=-1 && p!=-1){
        cout << solve(n, p) << 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, 3,114514) {
		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+c] + prime[j+c];
			}
		}
		sort(ALL(v));
		cout << v[p - 1] << endl;
	}
	return 0;
}