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 substringtest(str):
    set_strings={"AB","BA"}
    if str[0:2] and str[-2:] in set_strings:
        return "YES"
    else:
        return "NO"
str1=input()
print(substringtest(str1))