Find unique number in columns and return column title

In the attached file are there three colums with unique data. I want to find the column where the number in A1 exist, and end up with the column name in A2. Do you have any suggestion regarding the formula I can use in A2.

I know that this can be solved by a lot of IF's, but I prefer something that is easier to check and review.

If you have just the three columns you could just run three separate tests but in general terms:

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try this formula in a2
=INDEX(C1:E1,MAX((C1:E11=A1)*COLUMN(C1:E11)-MIN(COLUMN(C1:E11))+1))
array entered with ctrl+shift+enter
so that {} appear around it
see link in my signature
hmm i see donkyote has posted a different way and noticed you probably use ; not , as separator very astute!