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<algorithm>
#include<vector>
using namespace std;

int main(){
  vector <int> result;
  int i,j,n,p,k,data[1000000],primenum[100001];
  for(i = 0; i < 100001; i++){
    data[i]=0;
    primenum[i]=0;
  }


  for(i = 2; i*i < 1000000; i++){
    if(data[i]==0){
      for(j = 2*i; j < 1000000; j+=i){
	data[j]=1;
      }
    }
  }
  data[0]=1;
  data[1]=1;
 
   while(1){
     result.clear();
    cin >> n >> p;
    if(n==-1 && p==-1)break;
    j = 0;
    for(i = n+1; i < 1000000; i++){
      if(data[i]==0){
	primenum[j]=i;
	j++;
	if(j==100)break;
      }
    }

    //for(i = 0; i < 30; i++){
    // cout <<"primenum[" << i << "]" << primenum[i] << endl;
    // }
      for(i = 0;i < 20; i++){
	for(k = i; k < 20; k++){
	result.push_back(primenum[i]+primenum[k]);
	//	cout << "primenum[i]" <<primenum[i] <<"primenum[k]" << primenum[k] << endl;
	}
      }

     
      
      sort(result.begin(),result.end());
      // for(i = 0; i < 100; i++){
      //	cout << "result[" <<i<< "]"<<result[i] << endl;
      // }
      cout << result[p-1] << endl;
      
    }
   return 0;
}

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>

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 <bits/stdc++.h>
#define N 1000000
using namespace std;

bool prime[N + 5] = {0};
int n, p, now;

void sprime() {
  int i, j;
  prime[0] = 1;
  prime[1] = 1;
  for(i = 2; i < sqrt(N); ++i)
    if(!prime[i])
      for(j = 2; i * j <= N; ++j) prime[i * j] = 1;
}

int main() {
  int i, j;
  sprime();
  while(1) {
    cin >> n >> p;
    if(n + p == -2) break;
    vector<int> v;
    while(v.size() < p)
      if(!prime[++n]) v.push_back(n);
    vector<int> ans;
    bool ch[N] = {0};
    for(i = 0; i < v.size(); ++i)
      for(j = i; j < v.size(); ++j) {
        // if(ch[v[i] + v[j]]) continue;
        ans.push_back(v[i] + v[j]);
        ch[v[i] + v[j]] = 1;
      }

    sort(ans.begin(), ans.end());
    // for(i = 0; i < ans.size(); ++i) cout << ans[i] << " ";
    cout << ans[p - 1] << endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
bool s[111111];
int main(void){
  s[0] = s[1] = true;
  for(int i = 2; i*i < 111111; i++){
    if(s[i]) continue;
    for(int j = i*2; j < 111111; j+=i){
      s[j] = true;
    }
  }

  int n,p;
  while(cin >> n >> p && ~n){
    vector<int> v;
    vector<int> c;
    for(int i = n+1; (int)v.size() < 100; i++){
      if(!s[i]) v.push_back(i);
    }
    for(int i = 0; i < 100; i++){
      for(int j = i; j < 100; j++){
	c.push_back(v[i]+v[j]);
      }
    }
    sort(c.begin(),c.end());
    cout << c[p-1] << endl;
  }
}

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

using namespace std;

int p[200001];

int main()
{
    p[0] = 1;
    p[1] = 1;
    for (int i = 4; i <= 200000; i += 2) p[i] = 1;
    
    for (int i = 3; i * i <= 200000; i += 2){
        if (!p[i]){
            for (int j = i * 3; j <= 200000; j += 2 * i) p[j] = 1;
        }
    }
    
    int N, P;
    
    while (scanf("%d %d", &N, &P) && ~N){
        vector<int> v, v2;
        
        for (int i = N + 1; ; i++){
            if (!p[i]) v.push_back(i);
            if (v.size() == 20) break;
        }
        
        for (int i = 0; i < 20; i++){
            for (int j = i; j < 20; j++){
                v2.push_back(v[i] + v[j]);
            }
        }
        sort(v2.begin(), v2.end());
        
        printf("%d\n", v2[P - 1]);
    }
    
    return (0);
}