Merge rows of a dataframe by adding the values of a row to a row above it if it is below a certain value

Question

I have a dataframe say: df = pd.DataFrame(np.random.randint(0, 50, 25).reshape(5, 5))

df =

39  1   3   23  6
19  44  18  23  33
41  19  12  34  41
17