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>
#include <cmath>
using namespace std;

#define rep(i,n) for(int i=0;i<(n);++i)
#define PB push_back
#define LIM 1200000
typedef long long ll;
typedef vector<ll> vint;
bool prime[LIM]; 
vint v;
int main(){
	rep(i,LIM) prime[i]=true;
	prime[0]=prime[1]=false;
	rep(i,(int)sqrt(LIM)){
		if(prime[i]){
			for(int j=i*i;j<LIM;j+=i){
				prime[j]=false;
			}
		}
	}
	rep(i,LIM){
		if(prime[i]){
			v.PB((ll)i);
		}
	}
	ll N,P;
	while(cin>>N>>P,N!=-1||P!=-1){
		vint ans;
		int c=0;
		rep(i,LIM){
			if(v[i]>N){
				c=i;
				break;
			}
		}
		for(int i=c;i<c+P;i++){
			for(int j=i;j<i+P;j++){
				ans.PB(v[i]+v[j]);
			}
		}
		// cout<<ans.size()<<endl;
		sort(ans.begin(),ans.end());
		cout<<ans[P-1]<<endl;
	}
	return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include<cstdio>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<utility>
#include<iomanip>
#include<vector>
#include<string>
#include<queue>
#include<stack>
#include<map>
#include<list>
#include<set>
#include<stdlib.h>
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define repp(i,k,n) for(int i=k;i<(int)n;i++)
using namespace std;
const int dx[4] = { 0, 1, 0, -1 }, dy[4] = { 1, 0, -1, 0 };
const int dX[8] = { 0, 1, 1, 1, 0, -1, -1, -1 }, dY[8] = { 1, 1, 0, -1, -1, -1, 0, 1 };
vector<long long> Prime;
void SieveOfEratosthenes(long long e) //setup vector<long long>Prime(~x)
{
	bool *x=new bool[e];
	for (long long i = 0; i <= e; i++)x[i] = false;
	for (long long i = 2; i <= e; i++)
	{
		if (x[i]);
		else
		{
			Prime.push_back(i);
			for (long long l = i; l <= e; l += i)x[l] = true;
		}
	}
	return;
}
struct XY
{
	int x;
	int y;
};
int in()
{
	int x;
	cin >> x;
	return x;
}
/*
(char)'1' - (int)48 = (int)1;
???1111181
*/
////////////////////////////////////////////////////



int main()
{
	SieveOfEratosthenes(500000);
	int n,p;
	while (cin>>n>>p&&n!=-1)
	{
		vector<long long>::iterator now=lower_bound(Prime.begin(),Prime.end(),n),ri,le;
		if (binary_search(Prime.begin(), Prime.end(), n))now++;
		vector<long long > ans;
		ri = now;
		le = now;
		rep(i, 200)
		{
			le = ri;
			rep(l, 200)
			{
				ans.push_back(*le + *ri);
				le++;
			}
			ri++;
		}
		sort(ans.begin(), ans.end());
		cout << ans[p-1] << endl;
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

int main() {
	vector<bool>x( 200000, 1 );
	vector<long long int>prime;
	x[0] = x[1] = 0;
	for( size_t i = 0; i < 200000; i++ ) {
		if( x[i] ) {
			prime.emplace_back( i );
			long long int j = 2;
			while( i*j < 200000 ) {
				x[i*j] = 0;
				j++;
			}
		}
	}
	long long int N, M;
	while( cin >> N >> M, N != -1 && M != -1 ) {
		auto now = upper_bound( prime.begin(), prime.end(), N ) - prime.begin();
		vector<long long int >memo;
		for( size_t i = 0; i < 101; i++ ) {
			for( size_t j = i; j < 101; j++ ) {
				memo.emplace_back( prime[now + i] + prime[now + j] );
			}
		}
		sort( memo.begin(), memo.end() );
		//memo.erase( unique( memo.begin(), memo.end() ), memo.end() );
		cout << memo[M - 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;
        
        for(int i = ptr + m - 1; i >= ptr; i--)
        {
            for(int j = ptr + m - 1; j >= i; j--)
            {
                c.push_back(prime[i] + prime[j]);
            }
        }
        
        sort(c.begin(), c.end());
         
        printf("%d\n", c[m - 1]);
    }
     
    return 0;
}