Formula field IF

Hello,
I'm trying to solve the issue with automatic set of STRING (or number) in the custom field depending of ZIP codes.
I used Formula field
If(${Leads.Zip Code}=zip_code_here,value1,0)+If(${Leads.Zip Code}=zip_code_here,value2,0)+If(${Leads.Zip Code}=zip_code_here,value3,0)

Finally i should get
zip                               customfield
10500 or 10501 or 10502 =       value1
10400,10401,10402 =       value2
10900,10901,10902 =       value3