def main(): 
    inp1 = input()
    inp2 = input()
    
    if abs(len(inp1) - len(inp2)) >= 2:
        print("?")
    else:
        for i in range(0, len(inp1)):
            print(inp1[i], end='')
            if i >= len(inp2):
                break
            print(inp2[i], end='')
        print()

if __name__ == '__main__':
    main()