Stairway of Blocks

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A stairway is formed by stacking even blocks next to and on top of each other. If the stairway depicted above is 5 blocks in length and 4 blocks in height, with a thin step at the beginning that does not require a block, and the stairway is only 1 block in width, how many blocks will be required to build such a stairway 20 blocks in length?