You are given string *s*. Your task is to determine if the given string *s* contains two non-overlapping substrings "AB" and "BA" (the substrings can go in any order).
The only line of input contains a string *s* of length between 1 and 10<sup class="upper-index">5</sup> consisting of uppercase Latin letters.
def main():
    s = input()

    prev = str()

    i = 0

    while i < len(s) - 1:
        ss = s[i:i + 2]
        if ss not in {"AB", "BA"}:
            i += 1
            continue
        if ss == prev:
            i += 2
            continue
        if ss == prev:
            i += 1
        elif prev == "AB" and ss == "BA":
            print("YES")
            return
        elif prev == "BA" and ss == "AB":
            print("YES")
            return
        prev = ss
        if ss in {"AB", "BA"}:
            i += 1
        i += 1

    print("NO")


main()
