89. Serial-In Parallel-Out Register

How do you plan to solve it?

module sipo4 (
    input        CLK,
    input        RST,
    input        serial_in,
    output reg [3:0] Q
);
    // Write your code here
    always @( posedge CLK or posedge RST )
    begin
        if( RST )
            Q   <= 4'b0000;
        else
            Q   <= { serial_in, Q[3:1]};
    end
endmodule