import java.io.*;
import java.net.*;

class CalculateServer {
    private ServerSocket listener;
    private CalculateLogger logger;

    public CalculateServer( int port ) throws IOException {
	/* determine the address of the server and connect to it */
	listener = new ServerSocket( port );
        logger = new CalculateLogger("calc.log");
    }

    public void serve() throws IOException {
        while ( true ) {
	    Socket sock = listener.accept();
            logger.report("accept: " + sock );
	    try {
		Calculator calc =
                    new Calculator(
                        sock.getInputStream(),
                        sock.getOutputStream() );
		calc.run();
	    }
	    catch( IOException  e ) {
                throw new RuntimeException( e );
	    }
	    sock.close();
            logger.report("close: " + sock );
	}
    }

    public static void main( String[] args ) {
	int port = 0;
	String host = null;
	try {
	    port = Integer.parseInt( args[0] );
	}
	catch( NumberFormatException e ) {
	    System.out.println("bad port number");
	    System.exit(0);
	}
	catch( IndexOutOfBoundsException e ) {
	    System.out.println("usage: java CalculateServer port");
	    System.exit(0);
	}

	try {
	    CalculateServer server = new CalculateServer( port );
	    server.serve();
	}
	catch( IOException e ) {
	    System.out.println("io error:" + e);
	    System.exit(0);
	}
    }
}

class Calculator {
    private DataInputStream requests;
    private DataOutputStream replys;
    
    public Calculator( InputStream in, OutputStream out ) {
	requests = new DataInputStream( new BufferedInputStream( in ));
	replys = new DataOutputStream( new BufferedOutputStream( out ));
    }

    public void run() {
	try {
	    while( true ) {
		int cmd = requests.readInt();
		if ( cmd == CalculatorCommands.EXIT ) {
		    break; 
		}
		else if ( cmd == CalculatorCommands.ADD ) {
		    replys.writeInt(
                        requests.readInt() + requests.readInt() );
		    replys.flush();
		}
		else if ( cmd == CalculatorCommands.MULT ) {
		    replys.writeInt(
                        requests.readInt() * requests.readInt() );
		    replys.flush();
		}
		else if ( cmd == CalculatorCommands.SUBTRACT ) {
		    replys.writeInt(
                        requests.readInt() - requests.readInt() );
		    replys.flush();
		}
		else if ( cmd == CalculatorCommands.DIVIDE ) {
		    replys.writeInt(
                        requests.readInt() / requests.readInt() );
		    replys.flush();
		}
		else {
		    // unkown command, give up
		    break;
		}
	    }
	    requests.close();
	    replys.close();
	}
	catch( IOException e ) {
	    // just give up right now
            throw new RuntimeException( e );
	}
    }
}