The Flipping Problem !

Problem description. Ankit has corridor of N doors, Some doors are open and some doors are closed. Ankit thinks that the corridor is clean if all the doors are in the same state(i.e. Either open or close). In one step you can flip any segment of consecutive doors. After flipping a segment, all open doors will be closed and vice-versa What is the minimum number of steps to make the clean? Input