Janice can type 6 sentences per minute. Today at work, Janice continued working on a paper she started typing yesterday. She typed for 20 minutes, took a break, and typed 15 minutes longer. She then had to erase 40 sentences she had typed incorrectly. After a meeting, she typed for 18 minutes more. In all, the paper had 536 sentences by the end of today. How many sentences did she start with today?
Please reason step by step, and put your final answer within \boxed{}.
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