Calculate date based on number

I am trying to create a simple form but can´t find the correct way.

I have af form with two fields. field 1 is a number field and field 2 is a calculated field.

when a number is entered in field 1, I want to display a date in field 2 calculated as 1. january +/- the number of days entered in field 1.

e.g. number entered in field 1 is 5= date displayed in field 2 displays 5. january
and -5 entered in field 1 displays 27. december

 

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