Have the function

take the stx parameter being passed and return the smallest number you can get through the following reduction method. The method is: Only the letters a$,$ b $,$ and c will be given in str and you must take two difierent adjacent characters and replace it with the thilrd. For example $"$ac$"$ can be replaced with $"$b$"$ but $"$aa$"$ cannot be replaced with anything. This method is done repeatedy untill the sting cannot be further reduced and the length of the resulting sting ${?}^s$ st be outputed.