import machine

# -------------------------
# State definitions
# -------------------------
A = 0
B = 1
C = 2
D = 3

# -------------------------
# FSM state variable
# -------------------------
state = A   # initial state

# -------------------------
# FSM function
# -------------------------
def fsm(input_bool):
    global state

    if state == A:
        print("A", end="")
        state = B if input_bool else C

    elif state == B:
        print("B", end="")
        state = C if input_bool else D

    elif state == C:
        print("C", end="")
        state = B if input_bool else A

    elif state == D:
        print("D", end="")
        state = A if input_bool else C

inputs = [True, False, True, True, False, False, True]

for i in inputs:
    fsm(i)

print()  # newline