input: Write a python function to find the maximum sum of a contiguous subarray.
  assert max_sum_contiguous_subarray([-2,1,-3,4,-1,2,1,-5,4]) == 6
  assert max_sum_contiguous_subarray([1,2,3,4,5]) == 15
  assert max_sum_contiguous_subarray([-1,-2,-3,-4]) == -1
output: def max_sum_contiguous_subarray(nums):
      max_sum = current_sum = nums[0]
      for num in nums[1:]:
          current_sum = max(num, current_sum + num)
          max_sum = max(max_sum, current_sum)
      return max_sum