import isel.leic.usbio.*;

public class lic {

	public static int CLK = 0x01;

	public static void main(String[] args) {
		while((~UsbPort.in() & 0x0f) != 0){
			if((~UsbPort.in() & 0x0f) != 0x0f){
				UsbPort.out(CLK);
				UsbPort.out(~CLK);
			}
			else
				if((~UsbPort.in() & 0x0f) == 0x0f){
				UsbPort.out(~CLK);
				UsbPort.out(CLK);
				}

		}

	}

}