Problem Statement

We have $N$ dice arranged in a line from left to right. The $i$-th die from the left shows $p_i$ numbers from $1$ to $p_i$ with equal probability when thrown.

We will choose $K$ adjacent dice, throw each of them independently, and compute the sum of the numbers shown. Find the maximum possible value of the expected value of this sum.

Constraints

• $1 ≤ K ≤ N ≤ 200000$
• $1 ≤ p_i ≤ 1000$
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

N K
p_1 ... p_N

Output

Print the maximum possible value of the expected value of the sum of the numbers shown.

Your output will be considered correct when its absolute or relative error from our answer is at most $10^{-6}$.