can anyone explain the output of this program

Given the following fragment of code, how many tests are required for 100% decision coverage?

if width > length then biggest_dimension = width if height > width then biggest_dimension = height end_if else biggest_dimension = length

if height > length then biggest_dimension = height

end_if

end_if

Answer to the above question is 4 . 4 test cases are required for 100% decision coverage. Can anyone tell the answer explanation for the following question?