import static java.lang.System.err;

public class Main {
	public static void main(String[] args) {
		java.io.PrintWriter out = new java.io.PrintWriter(System.out);
		new Main(out);
		out.flush();
		err.flush();
	}

	public Main(java.io.PrintWriter out) {
		try (java.util.Scanner sc = new java.util.Scanner(System.in)) {
			int A = Integer.parseInt(sc.next(), 2), B = Integer.parseInt(sc.next(), 2);
			out.println(A ^ B);
		}
	}
}