Salesforce: Validation rule for valid US States

Validation rule for Billing State to be of two characters and valid US state
OR(
LEN(BillingState) < 2,
NOT(
CONTAINS(
“AL:AK:AZ:AR:CA:CO:CT:DE:DC:FL:GA:HI:ID:” &
“IL:IN:IA:KS:KY:LA:ME:MD:MA:MI:MN:MS:MO:MT:NE:NV:NH:” &
“NJ:NM:NY:NC:ND:OH:OK:OR:PA:RI:SC:SD:TN:TX:UT:VT:VA:” &
“WA:WV:WI:WY”,
BillingState)))