3 ms·

arguably that assumes that the operator that each letter denotes is self inverse. in the general case, y⁻¹ t⁻¹ i⁻¹ l⁻¹ i⁻¹ b⁻¹ i⁻¹ t⁻¹ a⁻¹ p⁻¹ m⁻¹ o⁻¹ c⁻¹