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<cstdio>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<vector>
using namespace std;
int main(){
  const int NUM = 1000000;
  bool prime[NUM];
  prime[0] = false;
  prime[1] = false;
  for(int i=2;i<NUM;i++)
    prime[i] = true;
  for(int i=2;i*i<NUM;i++)
    for(int k=2;i*k<NUM;k++)
      prime[i*k]=false;

  int n,p,pn;
  while(true){
    cin >> n >> p;
    if (n==-1)
      break;
    int sum[p*p];
    for(int i=0;i<p*p;i++)
      sum[i] = 0;
    pn = n+1;
    for(int i=0;i<p;i++){
      while(!prime[pn])
	pn++;
      for(int j=0;j<p;j++){
	sum[j*p+i] += pn;
	sum[i*p+j] += pn;
      }
      pn++;
    }
    for(int i = 0;i<p*p;i++){
      if(i/p>i%p)
	sum[i] = 1000000;
    }
    
    sort(sum,sum+p*p);
    cout << sum[p-1] << endl;
  }
  return 0;
}

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

#define rep(i,n) for(int i=0;i<(n);i++)
using namespace std;

bool is_prime[200010];
int n,p;

void init() {
    rep(i,200010) is_prime[i]=true;
    is_prime[0]=is_prime[1]=false;
    for(int i=2;i<200010;i++) {
        if(is_prime[i]) for(int j=i+i;j<200010;j+=i) is_prime[j]=false;
    }
}

int next_prime(int m) {
    m++;
    while(true) {
        if(is_prime[m]) break;
        m++;
    }
    
    return m;
}

void solve() {
    vector<int> vec,ans;
    int t = n;
    for(int i=0;i<p;i++) {
        t = next_prime(t);
        vec.push_back(t);
        
    }
    for(int i=0;i<p;i++)  for(int j=i;j<p;j++) {
        ans.push_back(vec[i]+vec[j]);

    }
    sort(ans.begin(),ans.end());
    cout<<ans[p-1]<<endl;

}
int main() {
    init();

    while(cin>>n>>p) {
        if(n==-1 && p==-1) return 0;
        solve();
    }
}

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

using namespace std;

#define NMAX 100

int main(){

	int hurui[150000]={0};
	int prime[100000];
	int table[200275]={0};
	int cnt=0;
	int cou;

	hurui[0]=1,hurui[1]=1;
	for(int i=2;i<150001;i++){
		if(hurui[i]==0){
			prime[cnt]=i;
			cnt++;
			for(int j=i;j<150001;j+=i){
				hurui[j]=1;
			}
		}
	}

	cou=cnt;

	int n,p;

	while(1){
		cin>>n>>p;
		if(n==-1&&p==-1) break;
		cnt=0;
		while(1){
			if(n<prime[cnt]) break;
			cnt++;
		}
		for(int i=0;i<200275;i++) table[i]=0;
		for(int i=cnt;i<cou;i++){
			for(int j=i;j<cou;j++){
				if(prime[i]+prime[j]<200275){
					table[prime[i]+prime[j]]++;
				}
			}
		}	
		while(p>=0){
			p-=table[cnt];
			cnt++;
		}
		cout<<cnt-1<<endl;
	}
}

C++: #include <iostream>
#include <complex>
#include <sstream>
#include <string>
#include <algorithm>
#include <deque>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <vector>
#include <set>
#include <limits>
#include <cstdio>
#include <cctype>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
#define REP(i, j) for(int i = 0; i < (int)(j); ++i)
#define FOR(i, j, k) for(int i = (int)(j); i < (int)(k); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define REVERSE(v) reverse((v).begin(), (v).end())
typedef complex<double> P;
const int L = 1e8;
const int M = 30;

bool p[L];

void make_p(){
  REP(i, L) p[i] = true;
  p[0] = p[1] = false;
  for(int i = 2; i * i <= L; ++i){
    if(!p[i]) continue;
    for(int j = i + i; j < L; j += i) p[j] = false;
  }
}

int main() {
  make_p();
  int N, P;
  while(cin >>N >>P && N != -1){
    vector<int> _p(M), v;
    for(int i = N + 1, cnt = 0; cnt < M; ++i) if(p[i]) _p[cnt++] = i;
    REP(i, M) FOR(j, i, M) v.push_back(_p[i] + _p[j]);
    SORT(v);
    cout <<v[P - 1] <<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<vector>
#include<cmath>
#include<algorithm>
#define MAX 1000000
using namespace std;

void eratos ( int n, vector<int> &v){
    bool prime[MAX+1];
    for ( int i = 0; i <= n; i++ ) prime[i] = false;
    for ( int i = 3; i <= n; i += 2 ) prime[i] = true;
    prime[2] = true;
    int limit = (int)sqrt((double)n) + 1;
    for ( int i = 3; i <= limit; i += 2 ){
	if ( !prime[i] ) continue;
	for ( int j = i + i; j <= n; j += i ) prime[j] = false;
    }
    for ( int i = 0; i <=n; i++ ) if (prime[i]) v.push_back(i);
}

main(){
    int N, P;
    vector<int> primes;
    eratos(MAX, primes);

    int k;
    while(1){
	cin >> N >> P;
	if ( N == -1 && P == -1 ) break;
	int s = distance(primes.begin(), upper_bound(primes.begin(), primes.end(), N));

	vector<int> v;
	for ( int i = s; i < s+P; i++ ){
	    for ( int j = i; j < s+P; j++ ){
		v.push_back(primes[i] + primes[j]);
	    }
	}
	sort(v.begin(), v.end());
	cout << v[P-1] << endl;
    }
}