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 <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()

using namespace std;

typedef long long ll;
typedef pair<int, int> P;
const int MAX_N = (int)1e6 + 5;
bool p[MAX_N];
vector<int> prime;

void make_prime (void ){

	prime.clear();
	fill (p, p+MAX_N, true );
	p[0] = false;
	p[1] = false;
	for (int i = 2; i < MAX_N; i++ ){
		if (p[i] ){
			for (int j = 2*i; j < MAX_N; j+= i ){
				p[j] = false;
			} // end for
		} // end if
	} // end for
	rep (i, MAX_N )
		if (p[i] ) prime.push_back (i );
}
			
int main()
{
	ios_base::sync_with_stdio(0);
	make_prime ();
	int N, P;
	while (cin >> N >> P ){
		if (N == -1 && P == -1 ) break;
		vector<int> pp; pp.clear();
		rep (i, prime.size() ){
			if (prime[i] > N ) pp.push_back (prime[i] );
			if (pp.size() >= P ) break;
		} // end rep
		vector<int> res; res.clear();
		rep (i, P ){
			for (int j = i; j < P; j++ ){
				res.push_back (pp[i] + pp[j] );
			} // end for
		} // end rep
		sort (ALL (res ) );
		cout << res[P-1] << endl;
	} // end while
 
	return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define o(a) cout << a << endl
#define int long long
#define fi first
#define se second
using namespace std;
typedef pair<int, int> P;

const int MAX_N = 200010;
int prime[MAX_N];
bool is_prime[MAX_N + 1];
void sieve(int n){
    int p = 0;
    for(int i = 0; i <= n; i++) 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;
        }
    }
}


signed main(){
    int n, p;
    sieve(200000);
    while(1){
        cin >> n >> p;
        if(n == -1 && p == -1) break;
        int ans = 0;
        vector<int> d;
        set<int> st;
        int id = -1;
        rep(i, 0, 200010){
            if(prime[i] > n){
                id = i;
                break;
            }
        }
        rep(i, 0, 200){
            rep(j, i, 200){
                int sum = prime[id + i] + prime[id + j];
                // if(!st.count(sum)){
                    d.push_back(sum);
                    st.insert(sum);
                // }
            }
        }
        sort(all(d));
        cout << d[p - 1] << endl;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;

const int MAX_N = 1000000;

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

void eratos(int n) {
    int p = 0;
    for (int i = 0; i <= n; ++i) 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;
        }
    }
}

int main() {
    eratos(MAX_N);

    int N, P;

    while (cin >> N >> P, (N != -1 and P != -1)) {
        vector<int> t(110);
        int cnt = 0;

        for (int i=N+1; i<MAX_N; ++i) {
            if (is_prime[i]) t[cnt++] = i;
            if (cnt >= 105) break;
        }

        vector<int> tt;

        cnt=0;
        rep(i, 101) {
            for (int j=i; j<=100; ++j) {
                tt.push_back(t[i] + t[j]);
            }
        }

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

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

    }

}