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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;

import java.util.*;


public class Soly
{
    static final int INF = Integer.MAX_VALUE;

    static void mergeSort(int[] a,int [] c, int b, int e)
    {
        if(b < e)
        {
            int q = (b + e) >>1;
            mergeSort(a,c, b, q);
            mergeSort(a, c,q + 1, e);
            merge(a,c, b, q, e);
        }
    }


    static void merge(int[] a,int[]c, int b, int mid, int e)
    {
        int n1 = mid - b + 1;
        int n2 = e - mid;
        int[] L = new int[n1+1], R = new int[n2+1];
        int[] L1 = new int[n1+1], R1 = new int[n2+1];

        for(int i = 0; i < n1; i++) {
            L[i] = a[b + i];
            L1[i] = c[b + i];
        }
        for(int i = 0; i < n2; i++)  {
            R[i] = a[mid + 1 + i];
            R1[i] = c[mid + 1 + i];
        }
        L[n1] = R[n2] = INF;

        for(int k = b, i = 0, j = 0; k <= e; k++)
            if(L[i] <= R[j]){
                a[k] = L[i];
                c[k] = L1[i++];
            }

            else
            {
                a[k] = R[j];
                c[k] = R1[j++];
            }
    }
    static  ArrayList<Integer>ss,hh;
static int bs(int n){
    int s=0,e=hh.size()-1,mid=0,ans=-1;
    while (s<=e){
        mid=(e+s)>>1;
        if (hh.get(mid)>=n){
            ans=mid;
            e=mid-1;
        }else s=mid+1;
    }
    return ans;
}
        static ArrayList<Integer> div(int v) {
    ArrayList<Integer>ans= new ArrayList<>();
            for (int i = 1; i*i <=v ; i++) {
                if (v%i==0){
                    ans.add(i);
                    if ((v/i)!=i)
                    ans.add(v/i);
                }
            }
            return ans;
        }

    public static void main(String[] args) throws IOException {
        Scanner in = new Scanner(System.in);
        try (PrintWriter or = new PrintWriter(System.out)) {

            int n= in.nextInt(),k=in.nextInt();
            int [] a= new int[n];
            for (int i = 0; i < n; i++) a[i]=in.nextInt();
            int max=0, i=0;
            for(; i<n-k; ++i)
                max=Math.max(a[i]+a[2*(n-k)-1-i], max);
            for(; i<n; ++i)
                max=Math.max(a[i], max);
            or.println(max);


        }
    }











    static class Scanner {

        StringTokenizer st;
        BufferedReader br;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public long nextLong() throws IOException {
            return Long.parseLong(next());
        }

        public String nextLine() throws IOException {
            return br.readLine();
        }

        public double nextDouble() throws IOException {
            String x = next();
            StringBuilder sb = new StringBuilder("0");
            double res = 0, f = 1;
            boolean dec = false, neg = false;
            int start = 0;
            if (x.charAt(0) == '-') {
                neg = true;
                start++;
            }
            for (int i = start; i < x.length(); i++) {
                if (x.charAt(i) == '.') {
                    res = Long.parseLong(sb.toString());
                    sb = new StringBuilder("0");
                    dec = true;
                } else {
                    sb.append(x.charAt(i));
                    if (dec) {
                        f *= 10;
                    }
                }
            }
            res += Long.parseLong(sb.toString()) / f;
            return res * (neg ? -1 : 1);
        }

        public boolean ready() throws IOException {
            return br.ready();
        }

    }



}
class coooo implements Comparable<coooo> {
    String st;
    int s,h;

    public coooo(String f,int s, int h) {
        this.st=f;
        this.s = s;
        this.h = h;
        //this.ind = ind;
    }

    @Override
    public int compareTo(coooo o) {
       return Long.compare(1l*o.s*h,1l*s*o.h);
    }
}