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<string>
#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cmath>
#include<utility>
#include<set>
#include<complex>
#include<map>
#define vi vector<int>
#define vvi vector<vector<int> >
#define ll long long int
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vb vector<bool>
#define vc vector<char>
#define vs vector<string>
#define ld long double
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define loop(i,s,n) for(int i=s;i<n;i++)
#define all(in) in.begin(), in.end()
#define MAX 9e5
using namespace std;
typedef pair<int, int> pii;
int main(){
    vector<bool>Primecheck(MAX+1,true);
    vector<int>Primenumber(MAX+1,0); //Primearray
    int Primecounter =0;                  //Primearray counter;
    for(int i = 2; i<MAX+1;i++){
        if(Primecheck[i]){
            for(int j = 2;i*j<MAX;j++)
                Primecheck[i*j] = false;//?´???°??????Primearray???????´??????????????????°?????¨???false???
            Primenumber[Primecounter] = i;
            Primecounter++;
        }
    }
    int n,m;
    while(cin>>n>>m,n+m>=0){
        int cnt=0;
        for(int i=0; i<Primenumber.size();i++){
            if(Primenumber[i]>=n){cnt=i;break;}
        }
        vi v;
        for(int i=cnt; i<=cnt+m;i++){
            for(int j=i; j<=cnt+m;j++){
                v.push_back(Primenumber[i]+Primenumber[j]);
            }
        }
        sort(all(v));
        cout<<v[m-1]<<endl;
    }

}

C++: #include<iostream>
#include<algorithm>
using namespace std;

bool e[100010];

void erato(){
	fill(e, e+150010, true);
	e[0] = e[1] = false;

	for(int i=0; i < 150010; i++){
		if(!e[i]) continue;
		for(int j=i+i; j < 150010; j += i){
			e[j] = false;
		}
	}
}

int main(){
	erato();

	int n, p;
	int primeNumbers[100];
	int addPrimeNumbers[100010];
	while(cin >> n >> p, n != -1 && p != -1){
		while(1){
			if(e[++n]) break;
		}
		for(int i=0; i < p; n++){
			if(e[n]){
				primeNumbers[i] = n;
				i++;
			}
		}
		int countPrimeNumbers = 0;
		for(int i=0; i < p; i++){
			for(int j=i; j < p; j++){
				addPrimeNumbers[countPrimeNumbers] =  primeNumbers[i] + primeNumbers[j];
				countPrimeNumbers++;
			}
		}
		sort(addPrimeNumbers, addPrimeNumbers + countPrimeNumbers);

		cout << addPrimeNumbers[p-1] << endl;
	}
}

C++: #include<bits/stdc++.h>
using namespace std;
int main(){
  bitset<1000000> bit;
  vector<int> prime;
  bit.set();
  for (int i = 2; i <= 1000000;i++){
    if(bit[i]==1){
      prime.push_back(i);
      for (int j = i * 2; j <= 1000000;j+=i){
        bit[j] = 0;
      }
    }
  }

  while(1){
    int n, p;
    cin >> n >> p;
    if(n==-1&&p==-1){
      break;
    }
    vector<int> sum;
    int index = 0;
    while(prime[index]<=n){
      index++;
    }
    for (int i = index; i - index < p;i++){
      for (int j = i; j - index < p;j++){
        sum.push_back(prime[i] + prime[j]);
      }
    }
    sort(sum.begin(), sum.end());
    cout << sum[p - 1] << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

vector<int> Prime(1000000),Matsuzaki(1000);

int judge(int n){
  if(n<2)return 0;
  if(n==2)return 1;
  if(n%2==0)return 0;
  for(int i=3;i<=n/i;i+=2){
    if(n%i==0)return 0;
  }
  return 1;
}

int main()
{
  int a=0,b=0,N,P,ii;
  for(int i=2;i<1000000;i++){
    if(judge(i))Prime[b++]=i;
  }
  while(1){
    cin>>N>>P;
    if(N==-1&&P==-1)break;
    a=0; 
    for(int i=0;i<b;i++){
      if(Prime[i]>N){
	ii=i;
	break;
      }
    }
    for(int i=ii;i<ii+100;i++){
      for(int j=i;j<ii+100;j++){
	Matsuzaki[a]=Prime[i]+Prime[j];
	a++;
      }
    }
    sort(Matsuzaki.begin(),Matsuzaki.begin()+a);
    cout<<Matsuzaki[P-1]<<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = uint32_t;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

vector<int> get_prime(int n){
    if(n <= 1) return vector<int>();
    vector<bool> iscomp(n+1);
    vector<int> prime;
    for (int i = 2; i <= n; ++i) {
        if(!iscomp[i]) prime.emplace_back(i);
        for (auto &&j : prime){
            if((ll)i*j > n) break;
            iscomp[i*j] = true;
            if(i % j == 0) break;
        }
    }
    return prime;
}
int main() {
    int n, p;
    auto x = get_prime(200000);
    while(cin >> n >> p, n != -1 && p != -1){
        vector<int> v;
        int cur = upper_bound(x.begin(), x.end(), n) - x.begin();
        for (int i = 0; i < p; ++i) {
            v.emplace_back(x[cur+i]);
        }
        vector<int> ans;
        for (int i = 0; i < p; ++i) {
            for (int j = i; j < p; ++j) {
                ans.emplace_back(v[i]+v[j]);
            }
        }
        sort(ans.begin(), ans.end());
        cout << ans[p-1] << "\n";
    }
    return 0;
}