module top_module(
    input in,
    input [1:0] state,
    output [1:0] next_state,
    output out); //

    parameter A=0, B=1, C=2, D=3;

    // State transition logic: next_state = f(state, in)
    always@(*)
        begin
            case(state)
                A:begin
                    next_state<=(in)?B:A;
                end
                B:
                    next_state<=(in)?B:C;
                C:
                    next_state<=(in)?D:A;
                D:
                    next_state<=(in)?B:C;
            endcase
        end

    // Output logic:  out = f(state) for a Moore state machine
    always@(state)
        begin
            if(state==D)
                out<=1;
            else
                out<=0;
        end

endmodule