71. As shown in the figure, Xi Xi draws a "square spiral" on a piece of paper, starting from the lower left corner and drawing line segments in the direction of the arrows with lengths of $1 \mathrm{~cm}, 1 \mathrm{~cm}, 1 \mathrm{~cm}, 1 \mathrm{~cm}, 2 \mathrm{~cm}, 2 \mathrm{~cm}, 1 \mathrm{~cm}, 3 \mathrm{~cm}, 3 \mathrm{~cm}, \ldots \ldots$. When Xi Xi finishes drawing the 100th line segment, the total length of this "spiral line" is $\qquad$ cm.
Reference answer: 1156
Checkpoint: Mathematical principle of finding patterns