module cycle(
    input button,
    output [3:0] leds
    );

reg [3:0] state;
assign leds = state;
initial begin
	state = 4'b1000;
end
always begin
	if (button) begin
		case (state)
			4'b1000: state <= 4'b0100;
			4'b0100: state <= 4'b1000;
		endcase
	end
end
endmodule