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 <sstream>
#include <fstream>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cmath>
using namespace std;

typedef long long Int;

const int SQRTN = 1<<16; // upperbound of sqrt(H)
vector<Int> segmentSieve(Int L, Int H) {
  static int p[SQRTN], lookup = 0;
  if (!lookup) {
    for (int i = 2; i < SQRTN; ++i) p[i] = i;
    for (int i = 2; i*i < SQRTN; ++i)
      if (p[i])
        for (int j = i*i; j < SQRTN; j += i)
          p[j] = 0;
    remove(p, p+SQRTN, 0);
    lookup = 1;
  }
  vector<Int> table(H - L);
  for (Int i = L; i < H; ++i) table[i - L] = i;
  for (int i = 0, j; p[i] * p[i] < H; ++i) { // O( \sqrt(H) )
    if (p[i] >= L) j = p[i] * p[i];
    else if (L % p[i] == 0) j = L;
    else                    j = L - (L % p[i]) + p[i];
    for (; j < H; j += p[i]) table[j-L] = 0;
  }
  return table;
}

int main() {
    int n, p;
    while ( cin >> n >> p ) {
        if ( n == -1 && p == -1 ) break;
        if ( n < 2 ) n = 2;
        vector <Int> T = segmentSieve( n, n+1000 );
        vector <Int> P;
        for ( int i = 0; i < (int)T.size(); i++ ) {
            if ( T[i] != 0 ) {
                P.push_back( n+i );
            }
        }
        int N = P.size();
        vector <Int> X;
        for ( int i = 0; i < min( 200, N ); i++ ) {
            for ( int j = i; j < min( 200, N ); j++ ) {
                X.push_back( P[i] + P[j] );
            }
        }
        sort( X.begin(), X.end() );
        cout << X[p-1] << endl;
    }
    return 0;
}

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

using namespace std;

typedef long long ll;
typedef vector<int> vint;
typedef pair<int, int> pii;

#define abs(a) ((a) < (0)? -(a):(a))
#define rep(i, n) REP(i, 0, (n))
#define REP(i, a, n) for(int i=(a); i<(n); i++)
#define pb push_back

int N = 110000;
bool is_prime[110000];

void set_prime() {
    rep(i, N) is_prime[i] = true;
    is_prime[0] = is_prime[1] = false;
    REP(i, 2, sqrt(N)) {
        if(is_prime[i]) {
            for(int j=0; i*(j+2)<N; j++) {
                is_prime[i*(j+2)] = false;
            }
        }
    }
}

int main() {
    set_prime();
    int n, p;
    while(cin>>n>>p, n+p>0) {
        vint v;
        for(int i=n+1, j = 0; j<20; i++) {
            if(is_prime[i]) j++, v.pb(i);
        }
        vint w;
        rep(i, v.size()) REP(j, i, v.size()) {
            w.pb(v[i]+v[j]);
        }
        sort(w.begin(), w.end());
        cout << w[p-1] << endl;
    }
}

C++: #include <stdio.h>
#include <cctype>
#include <limits.h>
#include <math.h>
#include <complex>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <sstream>
#include <algorithm>
#include <iomanip>
#include <iostream>

#define VARIABLE(x) cerr << #x << "=" << x << endl
#define BINARY(x) static_cast<bitset<16> >(x);
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define REP(i,m,n) for (int i=m;i<(int)(n);i++)
#define if_range(x, y, w, h) if (0<=(int)(x) && (int)(x)<(int)(w) && 0<=(int)(y) && (int)(y)<(int)(h))

const int INF = 1e9;
const double EPS = 1e-8;
const double PI = 3.14159;
int dx[4]={0, 1, 0, -1}, dy[4]={-1, 0, 1, 0};
using namespace std;
typedef long long ll;
//typedef pair<int, int> P;
struct P {
	int x, y, n;
	P(int n, int x, int y):n(n), x(x), y(y){}
	P(){}
};

/** Problem2150 : Matsuzaki Number **/
const int MAX = 1e6;
int main()
{
	bool isPrime[MAX];
	memset(isPrime, 1, sizeof(isPrime));
	isPrime[0]=false, isPrime[1]=false;
	for (int i=2; i<MAX; i++) {
		if (isPrime[i]) {
			for (int j=2; i*j<MAX; j++) {
				isPrime[i*j]=false;
			}
		}
	}
	
	while (true) {
		int N, P;
		cin>>N>>P;
		if (N==-1&&P==-1) break;
		
		vector<int> pp;
		for (int i=N; i<MAX&&pp.size()<=P; i++) {
			if (isPrime[i])
				pp.push_back(i);
		}
		
		vector<int> m;
		for (int i=0; i<pp.size(); i++) {
			for (int j=i; j<pp.size(); j++) {
				m.push_back(pp[i]+pp[j]);
			}
		}
		
		sort(m.begin(), m.end());
		cout << m[P-1] << endl;
	}
}

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; int r = min(20, m) - 1;
        
        for(int i = ptr + r; i >= ptr; i--)
        {
            for(int j = ptr + r; j >= i; j--)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
        
        sort(c.begin(), c.end());
         
        printf("%d\n", c[m - 1]);
    }
     
    return 0;
}