func findMaxAverage(nums []int, k int) float64 {
	n := len(nums)
	max := 0.0
	for i := 0; i < k; i++ {
		max += float64(nums[i])
	}
	sum := max
	for i := k; i < n; i++ {
		sum += float64(nums[i]) - float64(nums[i-k])
		if max < sum {
			max = sum
		}
	}
	return max / float64(k)
}