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 s i . In fact, he keeps his cowbells sorted by size, so s i - 1 ≤ s i 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 .

输入描述:

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.

输出描述:

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.

备注:

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}.