Need help for poster resolution

Hi everyone first time posting here Ive got a question to all you designpros:

I have to create a poster which has the measurment of 120cm x 60cm and I would like to know the best DPI and resolution for it. Ive searched a bit on the internet but it was mostly very complicated stuff about different dpis on different distances. So this poster I/we create will be printed out and will hang in a big mall. So if anyone could help me out here with a response I'd be very thankfull :) see you guys soon :D

EDIT: I should tell you that people might look at it from a distance of 2meters. :)

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