Maximum Average Segment

You are given an array of $N$ integers. Among all contiguous subarrays whose length is at least $K$, find the one with the largest average and report that average.

The average of a subarray is the sum of its elements divided by the number of elements.

The first line contains two integers $N$ and $K$ separated by a space ($1 \le N \le 3 \times 10^5$, $1 \le K \le N$).

The second line contains the array elements $a_1, a_2, \dots, a_N$ separated by spaces ($1 \le a_i \le 10^6$).

Let $A$ be the largest possible average. Print $A$ on one line, truncated to six digits after the decimal point. That is, print $\lfloor A \times 10^6 \rfloor$ split into an integer part and six decimal digits. Digits past the sixth are cut off, never rounded.

$A$ is a rational number whose denominator is at most $N$, so integer arithmetic computes it exactly. Print all six decimal digits even when they are zeros.