Moving between Floors

Did you know that the world's tallest structure is Burj Khalifa in Dubai ? To survive when the world ends, Mr.Turing thinks that he should climb one of those skyscrapers ( tall buildings ). There are N tall buildings numbered b_1, b_2, ... , b_N in that order and b_i and b_i+1 are adjacent to each other for 1 ≤ i Turing is afraid that some buildings may still collapse and so he lists down the brid