import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String X = sc.next();
		String Y = sc.next();
		
		int diff = X.length() - Y.length();
		
		if (0 <= diff || diff <= 1) {
			char[] S = new char[X.length() + Y.length()];
			for (int i = 0; i < X.length(); i++) {
				S[2 * i] = X.charAt(i);
			}
			for (int i = 0; i < Y.length(); i++) {
				S[2 * i + 1] = Y.charAt(i);
			}
			for (char s: S) {
				System.out.print(s);
			}
			System.out.println();
		} else {
			System.out.println("?");
		}
	}
}