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 <algorithm>
using namespace std;
const int MAX = 10000000;
vector<int> sosuu(MAX,1);
vector<int> sosuuMap;
vector<int> sosuuSum;
int n,m;
void makeSosuu(){
  sosuu[1] = 0;
  for(int i = 2;i <= MAX;i++){
    if(sosuu[i] == 1){
      sosuuMap.push_back(i);
      for(int j = i + i;j <= MAX;j = j + i){
	sosuu[j] = 0;
      }
    }
  }
  
}
void makeSumSosuu(){
  sosuuSum = vector<int>();
  int keep;
  for(int i = 0;i <= MAX;i++){
    if(sosuuMap[i] > n){
      keep = i;
      break;
    }
  }
  for(int i = keep;i <= keep+100;i++){
    for(int j = i;j <= keep+100;j++){
     	sosuuSum.push_back(sosuuMap[i]+sosuuMap[j]);
    }
    
    sort(sosuuSum.begin(),sosuuSum.end());
  }
}
int main(){

  makeSosuu();

  while(1){
    cin >> n >> m;
    if(n == -1 && m == -1)break;
    makeSumSosuu();
    cout << sosuuSum[m-1] << endl;
  }
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool so[10000001];

int main() {

  so[0] = so[1] = 1;
  for(int i=2;i*i<=10000000;i++){
    if(so[i] == 0) {
      for(int j=2;j<=10000000/i;j++) so[i*j] = 1;
    }
  }

  while(1) {
    int n,p;
    cin >> n >> p;
    if(n == -1 && p ==-1) break;

    int cnt = 0;

    int a[101] = {};
    for(int i=n+1;cnt<=p;i++) if(so[i] == 0) a[cnt] = i,cnt++;
    


    int c =0;
    bool flg[101][101];
    for(int i=0;i<=p;i++)
      for(int j=0;j<=p;j++) flg[i][j] = 0;
    vector <int> b;
    for(int i=0;i<=p;i++)
      for(int j=0;j<=p;j++) {
	if(flg[i][j] == 1) continue;
	flg[i][j] = 1;
	flg[j][i] = 1;
	int sum = a[i]+a[j];
	b.push_back(sum);
	c++;
      }

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

    // for(int i=0;i<p;i++) cout << b[i] <<endl;
    cout << b[p-1] <<endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

int main() {
  int M = 1e6;
  std::vector<int> p(M+1, 1);
  p[0] = p[1] = 0;
  for (int i = 2; i*i <= M; ++i) {
    if (!p[i]) continue;
    for (int j = i*i; j <= M; j += i)
      p[j] = 0;
  }

  std::vector<int> q;
  for (int i = 2; i <= M; ++i)
    if (p[i]) q.push_back(i);

  while (true) {
    int N, P;
    scanf("%d %d", &N, &P);
    if (N == -1 && P == -1) break;

    std::vector<int> C;
    auto it = std::upper_bound(q.begin(), q.end(), N);
    for (int i = 0; i < P; ++i)
      for (int j = 0; j <= i; ++j)
        C.push_back(it[i]+it[j]);

    std::sort(C.begin(), C.end());
    printf("%d\n", C[P-1]);
  }
}

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

using namespace std;

int N, P;

vector<int> nprimes;

bool isPrime(int x) {
	for (int i=2; i*i<=x; i++) if (x%i==0) return false;
	return x>1;
}
void nPrimes() {
	nprimes.clear();
	for (int i=N+1; ; i++) {
		if (isPrime(i)) nprimes.push_back(i);
		if (nprimes.size() > P) break;
	}
}

void solve() {
	vector<int> all;
	int size = (int)nprimes.size();
	for (int i=0; i<size; i++) {
		for (int j=i; j<size; j++) {
			all.push_back(nprimes[i] + nprimes[j]);
		}
	}
	sort(all.begin(), all.end());
	cout << all[P-1] << endl;
}

int main() {
	while (1) {
		cin >> N >> P; if (N==-1 && P==-1) break;
		nPrimes();
		solve();
	}
	
	return 0;
}

C++: #include<cstdio>
#include<cstring>
#include<queue>

using namespace std;

char prime[200005];

int main(void) {
    memset(prime, 1, sizeof(prime));
    prime[0] = prime[1] = 0;
    for(int i=2; i<=1e5+1e3; i++) {
        if(!prime[i]) continue;
        for(int j=2; i*j<=1e5+1e3; j++)
            prime[i*j] = 0;
    }

    while(true) {
        int n,p;
        scanf("%d%d", &n, &p);
        if(n == -1) break;

        priority_queue<int,vector<int>,greater<int> > pool;
        for(int i=n+1; i < n+2000; i++) {
            if(!prime[i]) continue;
            for(int j=i; j < i+2000; j++) {
                if(!prime[j]) continue;
                pool.push(i+j);
            }
        }
        for(int i=0; i<p-1; i++)
            pool.pop();
        printf("%d\n", pool.top());

    }
}