Nina decided to track her water intake over a week to ensure she was staying hydrated. She knows she drank a total of 56 liters for the week. She recorded that she drank 8 liters on Monday, 7 liters on Tuesday, 9 liters on Wednesday, and 6 liters on Thursday. On Friday and Saturday, she drank 10 liters each day. Unfortunately, she forgot to record her intake on Sunday. How many liters of water did she drink on Sunday? Let's think step by step and output the final answer within \boxed{}.
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