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 <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <sstream>

using namespace std;

int main(){
	
	int N = 200000;
	
	bool a[200000];
	
	for(int i = 0; i < N; i++){
		a[i] = true;
	}
	
	a[0] = false;
	a[1] = false;
	
	for(int i = 2; i < N; i++){
		if(a[i]){
			for(int j = i * 2; j < N; j += i){
				a[j] = false;
			}
		}
	}
	
	int P;
	
	while(true){
		
		cin >> N >> P;
		
		if(P == -1){
			break;
		}
		
		int primes[100];
		
		int count = 0;
		
		while(true){
			N++;
			if(a[N]){
				primes[count] = N;
				count++;
			}
			if(count == 100){
				break;
			}
		}
		
		vector<int> v;
		
		for(int i = 0; i < 100; i++){
			for(int j = i; j < 100; j++){
				v.push_back(primes[i] + primes[j]);
			}
		}
		
		sort(v.begin(), v.end());
		
		cout << v[P - 1] << endl;
		
	}
	
	return 0;
}

C++: #include<stdio.h>
int prime[1300001];

void isprime(void){
	int i,j,n,c;
	
	for(i = 4;i<1300001;i += 2)prime[i] = 1;
	
	for (i = 3;i * i <= 1300001;i += 2){
		if (prime[i] == 0){
			for (j = i + i; j <= 1300001; j += i){
				prime[j] = 1;
			}
		}
	}
}

int main(void){
	int n,i,a=0;
	int flag,p,j,k;
	isprime();
	while (scanf("%d%d",&n,&p),n!=-1&&p!=-1){
		a=0;
		flag=0;
		for(i = (n+1)*2;;i++){
			for(j = n+1;j < i;j++){
				for(k = j;j+k <= i;k++){
					if(j+k == i){
						if(prime[j]==0&&prime[k]==0){
							a++;
							if(a==p){
								printf("%d\n",i);
								flag=1;
								break;
							}
						}
					}
					if(flag)break;
				}
				if(flag)break;
			}
			if(flag)break;
		}
	}
	return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
#define REP(i, a, n) for(int i=a; i<n; i++)

bool prime[2000001];
void create_prime() {
	REP(i, 2, 2000001) prime[i] = true;

	for (int i = 2; i * i < 2000001; i++) {
		for (int j = 2 * i; j < 2000001; j += i) {
			prime[j] = false;
		}
	}
	return;
}
int main() {
	int N, P;
	create_prime();
	
	while (cin >> N >> P, N != -1 && P != -1) {
		vector<int> v, sum;
		REP(i, N + 1, 2000001) {
			if (prime[i]) v.push_back(i);
			if (v.size() > 2 * P + 1) break;
		}

		REP(i, 0, v.size()) {
			REP(j, i, v.size()) {
				sum.push_back(v[i] + v[j]);
			}
		}

		sort(sum.begin(), sum.end());
		cout << sum[P - 1] << endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> duo;

#define TT template<typename T>
TT T    sq(T x){ return x*x; }
TT int  ubnd(vector<T>& v,T x){ return upper_bound(v.begin(), v.end(), x) - v.begin(); }
TT int  lbnd(vector<T>& v,T x){ return lower_bound(v.begin(), v.end(), x) - v.begin(); }
TT void sort(T& v){ sort(v.begin(), v.end()); }
TT void revs(T& v){ reverse(v.begin(), v.end()); }
TT void uniq(T& v){ sort(v); v.erase(unique(v.begin(), v.end()), v.end()); }
TT void show(T& v,char d=' ',char e='\n'){for(int i=0;i<v.size();++i)cout<<v[i]<<((i==v.size()-1)?e:d);}
TT void inpt(vector<T>& v,int n){ v.reserve(n);for(int i=0;i<n;++i){T x; cin>>x; v.push_back(x);} }
TT T In(){ T x; cin >> x; return x; }

static inline void fast_io(){ ios::sync_with_stdio(0); cin.tie(0); }
static inline int in(){ int x; scanf("%d", &x); return x; }
static inline string instr(){ string x; cin >> x; return x; }
static const int dx[] = {0, 0, 1, -1, 1, 1, -1, -1};
static const int dy[] = {1, -1, 0, 0, 1, -1, 1, -1};

void build_primes(vector<bool>& bs, int n)
{
  bs.assign(n + 1, false);
  bs[0] = bs[1] = true;
  for (int i = 2; i * i <= n; i++){
    if (bs[i]) continue;
    for (int j = i * i; j <= n; j += i) bs[j] = true;
  }
}

int main()
{
  vector<bool> sieve;
  build_primes(sieve, 999999);
  vector<int> ps;
  for (int i = 0; i <= 999999; i++) if (!sieve[i]) ps.push_back(i);

  int n, p;
  while (n = in(), p = in(), ~p){
    int ui = ubnd(ps, n);
    vector<int> _v;
    for (int i = 0; i < 100; i++){
      for (int j = i; j < 100; j++){
        _v.push_back(ps[ui + i] + ps[ui + j]);
      }
    }
    sort(_v);
    printf("%d\n", _v[p - 1]);
  }
  return (0);
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string> 
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

int min_prime(int n);
int isprime(int n);

int main()
{
	int n, p;
	while(1){
		cin >> n >> p;
		if(n == -1 && p == -1) break;
		int prime_array[1000] = {0}, sum_array[50000] = {0};
		prime_array[0] = min_prime(n);
		for(int i = 0; i < (2 * p); i++){
			prime_array[i + 1] = min_prime(prime_array[i]);
		}
		int k = 0;
		for(int i = 0; i < (2 * p) + 1; i++){
			for(int j = i; j < (2 * p) + 1; j++){
				sum_array[k] = prime_array[i] + prime_array[j];
				k++;
			}
		}
		sort(sum_array, sum_array+k);
		cout << sum_array[p - 1] << endl;
	}
	return 0;
}

int min_prime(int n)
{
	while(++n){
		if(isprime(n)) break;
	}
	return n;
}

int isprime(int n)
{
	int ans = 0;
	if(n == 0 || n == 1) ans = 0;
	else if(n == 2) ans = 1;
	else {
		for(int i = 2; i < n; i++){
			if(i * i > n){
				ans = 1;
				break;
			}
			else if(n % i == 0){
				ans = 0;
				break;
			}
		}
	}
	return ans;
}