Kevin Sun wants to move his precious collection of n cowbells from Naperthrill to Exeter, where there is actually grass instead of corn. Before moving, he must pack his cowbells into k boxes of a fixed size. In order to keep his collection safe during transportation, he won't place more than two cowbells into a single box. Since Kevin wishes to minimize expenses, he is curious about the smallest size box he can use to pack his entire collection. 

Kevin is a meticulous cowbell collector and knows that the size of his i-th (1 ≤ i ≤ n) cowbell is an integer si. In fact, he keeps his cowbells sorted by size, so si - 1 ≤ si for any i > 1. Also an expert packer, Kevin can fit one or two cowbells into a box of size s if and only if the sum of their sizes does not exceed s. Given this information, help Kevin determine the smallest s for which it is possible to put all of his cowbells into k boxes of size s.

Input

The first line of the input contains two space-separated integers n and k (1 ≤ n ≤ 2·k ≤ 100 000), denoting the number of cowbells and the number of boxes, respectively.

The next line contains n space-separated integers s1, s2, ..., sn (1 ≤ s1 ≤ s2 ≤ ... ≤ sn ≤ 1 000 000), the sizes of Kevin's cowbells. It is guaranteed that the sizes si are given in non-decreasing order.

Output

Print a single integer, the smallest s for which it is possible for Kevin to put all of his cowbells into k boxes of size s.

Examples

Input

2 1
2 5


Output

7


Input

4 3
2 3 5 9


Output

9


Input

3 2
3 5 7


Output

8

Note

In the first sample, Kevin must pack his two cowbells into the same box. 

In the second sample, Kevin can pack together the following sets of cowbells: {2, 3}, {5} and {9}.

In the third sample, the optimal solution is {3, 5} and {7}.
import java.awt.*;
import java.awt.geom.Line2D;
import java.io.*;
import java.math.*;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.attribute.BasicFileAttributeView;
import java.nio.file.attribute.FileTime;
import java.util.*;
import java.util.List;


public class Main implements Runnable {
    
    int maxn = (int)2e5+111;
    int mod = (int)1e9+7;
    int inf = (int)1e9;
    int n,m,k;
    int a[] = new int[maxn];
    int b[] = new int[maxn];
    int c[] = new int[maxn];
    ArrayList<Integer> list = new ArrayList<Integer>();
    TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
    
    void solve() throws Exception {
    	
    	n = in.nextInt();
    	k = in.nextInt();
    	
    	int b[] = new int[k+1];
    	
    	for (int i=1; i<=n; i++) {
    		a[i] = in.nextInt();
    	}
    	
    	int r = n;
    	boolean toLeft = true;
    	while (r>0) {
    		if (toLeft) {
    			for (int i=k; i>=1; i--) {
    				b[i]+=a[r--];
    				if (r<=0) break;
    			}
    			toLeft = !toLeft;
    		} else {
    			for (int i=1; i<=k; i++) {
    				b[i]+=a[r--];
    				if (r<=0) break;
    			}
    			toLeft = !toLeft;
    		}
    	}
    	
    	int max = 0;
    	for (int i=1; i<=k; i++) {
    		max = Math.max(b[i],max);
    	}
    	
    	out.println(max);
    }  
    
	class Pair implements Comparable<Pair>{
        int x,y; 
        public Pair (int x, int y) {
            this.x = x;
            this.y = y;
        }

        @Override
        public int compareTo(Pair p) {
        	if (x>p.x) return 1;
        	else if (x==p.x) {
        		if (y>p.y) return 1;
        		else if (y==p.y) return 0;
        		else return -1;
        	} else {
        		return -1;
        	}
        
        }
    }

	String fileInName = "network";
	boolean file = false;
	boolean isAcmp = true;
    
    static Throwable throwable;
    public static void main (String [] args) throws Throwable {
        Thread thread = new Thread(null, new Main(), "", (1 << 26));
        thread.start();
        thread.join();
        thread.run();
        if (throwable != null)
            throw throwable;
    }
    
    FastReader in;
    PrintWriter out;

    public void run() {
    	String fileIn = "input.txt";
    	String fileOut = "output.txt";
    	
        try {
        	if (isAcmp) {
        		if (file) {
                    in = new FastReader(new BufferedReader(new FileReader(fileIn)));
                    out = new PrintWriter (fileOut);
                } else {
                    in = new FastReader(new BufferedReader(new InputStreamReader(System.in)));
                    out = new PrintWriter(System.out);
                }
        	} else if (file) {
                in = new FastReader(new BufferedReader(new FileReader(fileInName+".in")));
                out = new PrintWriter (fileInName + ".out");
            } else {
                in = new FastReader(new BufferedReader(new InputStreamReader(System.in)));
                out = new PrintWriter(System.out);
            }
            
            solve();
        } catch(Exception e) {
            throwable = e;
        } finally {
            out.close();
        }

    }
}

class FastReader {
    BufferedReader bf;
    StringTokenizer tk = null;

    public FastReader(BufferedReader bf) {
        this.bf = bf;
    }
    
    public String nextToken () throws Exception {
        if (tk==null || !tk.hasMoreTokens()) {
            tk = new StringTokenizer(bf.readLine());
        }
        if (!tk.hasMoreTokens()) return nextToken();
        else 
            return tk.nextToken();
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(nextToken());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(nextToken());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(nextToken());
    }
}