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 <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>

using namespace std;
#define REP(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define RREP(i, a) for(int (i) = (a) - 1; (i) >= 0; (i)--)
#define FORR(i, a, b) for(int (i) = (a) - 1; (i) >= (b); (i)--)
#define DEBUG(C) cerr << #C << " = " << C << endl;
using LL = long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<LL>;
using VVL = vector<VL>;
using VD = vector<double>;
using VVD = vector<VD>;
using PII = pair<int, int>;
using PDD = pair<double, double>;
using PLL = pair<LL, LL>;
using VPII = vector<PII>;
#define ALL(a) begin((a)), end((a))
#define RALL(a) rbegin((a)), rend((a))
#define SORT(a) sort(ALL((a)))
#define RSORT(a) sort(RALL((a)))
#define REVERSE(a) reverse(ALL((a)))
#define MP make_pair
#define FORE(a, b) for (auto &&a : (b))
#define FIND(s, e) ((s).find(e) != (s).end())
#define EB emplace_back

const int INF = 1e9;
const int MOD = INF + 7;
const LL LLINF = 1e18;

vector<int> sieve_of_eratosthenes(int n) {
    vector<bool> is(n + 1, true);
    vector<int> res;
    is[0] = false;
    is[1] = false;
    for (int i = 2; i <= n; i++) if (is[i]) {
        res.emplace_back(i);
        for (int j = i * 2; j <= n; j += i) {
            is[j] = false;
        }
    }
    return res;
}
VI primes;
void solve(int N, int P) {
    int start;
    REP(i, primes.size()) {
        if (primes[i] > N) {
            start = i;break;
        }
    }
    VI v;
    FOR(i, start, start + P + 1) {
        FOR(j, i, start + P + 1) {
            v.EB(primes[i] + primes[j]);
        }
    }
    SORT(v);
    int cnt = 0;
    FORE(e, v) {
        cnt++;
        //cerr << e << " ";
        if (cnt == P) {
            cout << e << endl;
            break;
        }
    }
    return;
}

signed main(void) {
    int n, m, p, a, b, c, x, y, z, q;
    string s;
    bool f = false;
    primes = sieve_of_eratosthenes(200000);
    while (cin >> n >> m, n != -1) {
        solve(n, m);
        //return 0;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;
const int N = 400000;
int for_erat[N];
vector<int> prime;
vector<int> v;
vector<int> res;


void erat(){
    for(int i = 0; i < N; i++){
        for_erat[i] = 1;
    }
    for(int i = 2; i < sqrt(N); i++){
        if(for_erat[i]){
            for(int j = 0; i * (j + 2) < N; j++){
                for_erat[i *(j + 2)] = 0;
            }
        }
    }

    for(int i = 2; i < N; i++){
        if(for_erat[i]){
            prime.push_back(i);
        }
    }
}

int main(){
	erat();
	//for(int i = 0; i < 10; i++) cout << prime[i] << endl;
while(1){//start
	//init
	v.clear();
	res.clear();


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

	//n以上の素数を15個見つける
	int idx = 0;
	while((int)v.size() != 20){
		if(prime[idx] > n) v.push_back(prime[idx]);
		idx++;
	}

	for(int i = 0; i < (int)v.size(); i++){
		for(int j = i; j < (int)v.size(); j++) res.push_back(v[i] + v[j]);
	}

	sort(res.begin(), res.end());
	//res.erase(unique(res.begin(), res.end()), res.end());

	cout << res[p-1] << endl;
	//for(int i = 0; i < (int)res.size(); i++) cout << res[i] << endl;


}//end
	return 0;

}

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

using namespace std;

int main(){
    vector<int> primes;
    bool isprime[200001];
    
    memset(isprime, true, sizeof(isprime));

    for(int i=2;i<200001;++i){
        if(isprime[i]){
            primes.push_back(i);
            for(int j=2;i*j<200001;++j){
                isprime[i*j] = false;
            }
        }
    }

    int N,P;
    while(cin >> N >> P){
        if(N == -1 && P == -1) break;
        vector<int> sums;
        vector<int>::iterator it,jt;
        it = upper_bound(primes.begin(), primes.end(), N);
        
        for(int i=0;i<100;++i){
            jt = it;
            for(int j=0;j<100;++j){
                sums.push_back((*it) + (*jt));
                ++jt;
            }
            ++it;
        }
        sort(sums.begin(), sums.end());
        cout << sums[P-1] << endl;
    }
}