ATM PIN Code Validation

ATM machines allow 4 or 6 digit PIN codes and PIN codes cannot contain anything but exactly 4 digits or exactly 6 digits. Your task is to create a function that takes a string and returns true if the PIN is valid and false if it's not.

Examples

validatePIN("1234") ➞ true

validatePIN("12345") ➞ false

validatePIN("a234") ➞ false

validatePIN("") ➞ false

Notes

• Some test cases contain special characters.
• Empty strings must return false.