Where to find my 2000 honda civic serial number?

Yesterday I bought it in cash, not with a dealer. I saw that the radio didn't work and read online that I need the number in order to input the code. I looked everywhere, side of the door on the dash in the papers, and I can't find it. The only paper I'm missing is the pink slip and the guy said he'll give me that today cause I was 100 short with the money so could it be there? Or should I just take it to my local honda dealer? What can I do to get the serial number?

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