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>
#include<set>
using namespace std;
int main(){
  int so[200000]={};
  int f;
  so[2]=1;
  for(int i=2;i<200000;i++){
    f=0;
    for(int j=2;j*j<=i;j++){
      if(i%j==0){
	f=1;
	break;
      }
    }
    if(f==0)so[i]=1;
  }
  int s,n;
  //
  while(1){
    cin >> s >> n;
    if(s==-1&&n==-1)break;
    vector<int>a;
    multiset<int>st;
    int k=s+1;
    for(int i=0;i<=n/2;i++){
      while(1){
	if(so[k]==0)k++;
	else{
	  a.push_back(k);
	  k++;
	  break;
	}
      }
    }
    int l=0;
  
    for(int i=0;i<a.size();i++){
      for(int j=0;j<=i;j++){
	st.insert(a[i]+a[j]);
	//	  cout << a[i]+a[j]<<endl;
      }
      //cout << a[i]*2<<endl;
    }
    int co=0;

    for( set<int>::iterator itr = st.begin(); itr != st.end() ; ++itr){
      co++;
      if(co==n){
	cout << *itr << endl;
	break;
      }
    }
  }
  return 0;
}

C++: #include<bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
const double EPS=1e-10;
const ll INF=1000000000;
const ll MAX=100010;
int prime[300010];
int main(){
        for(int i=0;i<300001;i++){
        prime[i]=1;
    }
    prime[0]=0;prime[1]=0;
    for(int i=2;i<=200000;i++){
        if(prime[i]==1){
            for(int j=i+i;j<=300000;j+=i){
                prime[j]=0;
            }
        }
    }
    vector<int> v;
    for(int i=0;i<=300000;i++){
        if(prime[i]){
            v.push_back(i);
        }
    }
    int n,p;
    while(cin>>n>>p,n+p>=0){
        int f=upper_bound(all(v),n)-v.begin();
        vector<int> ans;
        for(int i=0;i<=p;i++){
            for(int j=i;j<=p;j++){
                ans.push_back(v[f+i]+v[f+j]);
            }
        }
        sort(all(ans));
        cout<<ans[p-1]<<endl;
    }
}

C++: #include <cstdio>
#include <string.h>
using namespace std;

#define MAX (100000)

bool prime[MAX + 1];
int prime_sum[MAX * 2 + 1];

int main()
{
	prime[0] = prime[1] = false;
	for (int i = 2; i <= MAX; i++){
		prime[i] = true;
	}
	
	for (int i = 2; i * i <= MAX; i++){
		for (int j = i * i; j <= MAX; j += i){
			prime[j] = false;
		}
	}
	
	int N, P;
	
	while (scanf("%d %d", &N, &P), N + P != -2){
		int cnt = 0;
		int i = N * 2 + 2;
		
		memset(prime_sum, 0, sizeof(prime_sum));
		for (int k = N + 1; k <= MAX; k++){
			for (int l = k; l <= MAX; l++){
				if (prime[k] && prime[l]){
					prime_sum[k + l]++;
				}
			}
		}
		
		while (1){
			for (int j = 0; j < prime_sum[i]; j++){
				cnt++;
				printf("%d\n", i);
			}
			
			if (cnt >= P){
				break;
			}
			i++;
		}
		
		printf("%d\n", i);
	}
	
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
const int SIZE=10000000;
bool is_prime[SIZE];
int main() {
    memset(is_prime,-1,sizeof(is_prime));
    for(int i=2;i*i<SIZE;i++) {
        if(!is_prime[i]) continue;
        for(int j=i*2;j<SIZE;j+=i) is_prime[j]=0;
    }
    vector<int> prime;
    for(int i=2;i<SIZE;i++) if(is_prime[i]) prime.push_back(i); 
    int N,P;
    while(scanf("%d %d",&N,&P),N!=-1) {
        int pos=upper_bound(prime.begin(),prime.end(),N)-prime.begin();
        vector<int> L;
        for(int i=0;i<P;i++) {
            for(int j=i;j<P;j++) {
                L.push_back(prime[pos+i]+prime[pos+j]);
            }
        }
        sort(L.begin(),L.end());
        printf("%d\n",L[P-1]);
    }
}

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

using namespace std;

int main(void){
  vector<int>num,ans;
  int n,p,prime[1000001];

  for(int i=0;i<1000001;i++)prime[i]=0;
  prime[0]=prime[1]=1;

  for(int i=2;i*i<1000001;i++){
    if(prime[i]==0){
      for(int j=2*i;j<1000001;j+=i){
	prime[j]=1;
      }
    }
  }

  while(cin >> n >> p){
    if(n<0 && p<0)break;
    num.clear();
    ans.clear();

    for(int i=n+1;i<n+p+1000;i++)
      if(prime[i]==0)num.push_back(i);

    for(int i=0;i<num.size();i++){
      for(int j=i;j<num.size();j++){
	ans.push_back(num[i]+num[j]);
      }
    }
    sort(ans.begin(),ans.end());

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

  return 0;
}

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

#define loop(n, i) for(int i=0;i<n;i++)
#define all(v) v.begin(),v.end()
#define HERE cout << "HERE: " << __LINE__ << endl;
#define INSP(v) cout << v << " at " << __LINE__ << endl;

using namespace std;
typedef long long ll;


int main()
{
    int max = 110000;
    vector<int> mat(max, 1);
    vector<int> primes;
    for (int i=2; i<sqrt(max); i++) {
        if (mat[i]) {
            for (int j=i*2; j < max; j+=i) mat[j] = 0;
        }
    }
    for (int i=2; i<max; i++) {
        if (mat[i]) primes.push_back(i);
    }

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

        int start;
        for (int i = 0; i < primes.size(); i++) {
            if (n < primes[i]) {
                start = i;
                break;
            }
        }

        vector<int> nums;
        for (int i = start; i < start+100; i++) {
            for (int j = i; j < start+100; j++) {
                nums.push_back(primes[i]+primes[j]);
            }
        }

        sort(all(nums));
        cout << nums[p-1] << endl;

    }
}