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 <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>
#include <fstream>

using namespace std;

#define FOR(i,a,b) for(long long i=(a);i<(b);i++)
#define REP(i,N) for(long long i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define fi first
#define se second

#define PI acos(-1.0)
#define INF 10e15+9
#define EPS 1e-10
#define MAX_N 100100
#define MAX_M 100100

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<double, double> PD;
typedef pair<string, ll> PS;
typedef vector<ll> V;
typedef pair<P, char> PC;

int n, p;

bool is_prime[1000000];
int prime[1000000];
int field[10000][10000];

int main(){
	fill(is_prime, is_prime + 1000000, 1);
	is_prime[0] = 0;
	is_prime[1] = 0;
	int po = 0;
	for (int i = 0; i <= 101000; i++){
		if (is_prime[i]){
			prime[po++] = i;
			for (int j = 0; j <= 101000; j += i){
				is_prime[j] = 0;
			}
		}
	}
	while (cin >> n >> p&&n != -1 && p != -1){
		REP(i, po)REP(j, po)field[i][j] = 10000000;
		int ans = 0;
		REP(i, po){
			REP(j, po){
				
			}
		}
		cout << ans << endl;
	}
}

C++: #define _USE_MATH_DEFINES
#define INF 0x3f3f3f3f
#include <cstdio>
#include <iostream>
#include <sstream>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <stack>
#include <limits>
#include <map>
#include <string>
#include <cstring>
#include <set>
#include <deque>
#include <bitset>
#include <list>
#include <cctype>
#include <utility>
#include <unordered_map>

using namespace std;

typedef long long ll;
typedef pair <int,int> P;
typedef pair <int,P > PP;

int tx[] = {0,1,0,-1};
int ty[] = {-1,0,1,0};

static const double EPS = 1e-8;

static const int MAX_N = 1000000;
bool isPrime[MAX_N];

int Matsuzaki(int N,int P){
	vector<int> prime;
	for(int i=N+1;i<=N+100000;i++){
		if(isPrime[i]){
			prime.push_back(i);
			if(prime.size() >= 100) break;
		}
	}

	vector<int> compo;
	for(int i=0;i<prime.size();i++){
		for(int j=i;j<prime.size();j++){
			compo.push_back(prime[i]+prime[j]);
		}
	}

	sort(compo.begin(),compo.end());
	//unique(compo.begin(),compo.end());

	return compo[P-1];
}

int main(){
	int N,P;
	memset(isPrime,-1,sizeof(isPrime));

	isPrime[0] = false;
	isPrime[1] = false;

	for(int i=2;i<MAX_N;i++){
		if(!isPrime[i]) continue;

		for(int j=i+i;j<MAX_N;j+=i){
			isPrime[j] = false;
		}
	}

	while(~scanf("%d %d",&N,&P)){
		if(N==-1) break;
		printf("%d\n",Matsuzaki(N,P));
	}
}

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 > 15) { 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 <cmath>
using namespace std;

static const int INF = 1000000;

int isprime[200001];

void eratos(int n) {
	for (int i = 0; i < 200001; i++)
		isprime[i] = 1;
	
	isprime[0] = isprime[1] = 0;
	for (int i = 2; i <= sqrt(n); i++) {
		if (isprime[i]) {
			int j = i * 2;
			while (j <= n) {
				isprime[j] = 0;
				j += i;
			}
		}
	}
}

void sort(int a[]) {
	for (int i = 0; i < 1275; i++)
		for (int j = i; j > 0; j--)
			if (a[j-1] > a[j]) {
				int t = a[j-1];
				a[j-1] = a[j];
				a[j] = t;
			}
}

int main() {
	eratos(200000);
	while (1) {
		int n, p;
		cin >> n >> p;
		if (p == -1) break;
		
		int index;
		for (int i = n + 1; ;i++)
			if (isprime[i]) {
				index = i;
				break;
			}
		int nprime[50];
		nprime[0] = index;
		int t = 1;
		for (int i = index + 1; ; i++) {
			if (isprime[i]) {
				nprime[t] = i;
				t++;
			}
			if (t == 50) break;
		}
		
		
		int sum[1275] = {INF};
		t = 0;
		for (int i = 0; i < 50; i++) {
			for (int j = i; j < 50; j++) {
				sum[t] = nprime[i] + nprime[j];
				t++;
			}
		}
		
		sort(sum);
		
		cout << sum[p-1] << endl;
		
	}
	return 0;
}