#Write a program to find the maximum sum of a subarray within a given list, 
#where the subarray length is at most k.
def max_subarray_sum(nums, k):
    if k <= 0 or len(nums) == 0:
        return 0

    max_sum = float('-inf')
    current_sum = 0
    start = 0

    for end, num in enumerate(nums):
        current_sum += num

        if end - start + 1 > k:
            current_sum -= nums[start]
            start += 1

        if end - start + 1 == k:
            max_sum = max(max_sum, current_sum)

    return max_sum

# Example usage
nums = [1, 4, 2, 10, 2, 3, 1, 0, 20]
k = 4
print(max_subarray_sum(nums, k))  # 24