Problem Statement

You are given a sequence $P=(P_1,P_2,\dots,P_N)$ of length $N$. Takahashi and Aoki will play a game using the sequence $P$.

First, Takahashi will choose $K$ distinct integers $x_1,x_2,\dots,x_K$ from $1,2,\dots,N$.

Next, Aoki will choose an integer $y$ from $1,2,\dots,N$ with a probability proportional to $P_y$. That is, the probability that integer $y$ is chosen is $\dfrac{P_y}{\sum_{y'=1}^N P_{y'}}$. Then, Aoki's score will be $\displaystyle \min_{i=1,2,\dots,K} |x_i-y|$.

Takahashi wants to minimize the expected value of Aoki's score. Find the expected value of Aoki's score when Takahashi chooses $x_1,x_2,\dots,x_K$ so that this value is minimized, multiplied by $\sum_{y'=1}^N P_{y'}$. It is guaranteed that the value to be printed is an integer.

Constraints

• $1 \leq N \leq 5 \times 10^4$
• $1 \leq K \leq N$
• $0 \leq P_i \leq 10^5$
• $1 \leq \sum_{y'=1}^N P_{y'} \leq 10^5$
• All input values are integers.

Input

The input is given from Standard Input in the following format:

N K
P_1 P_2 \dots P_N

Output

Print the answer.