CODEFORCE 550A

cf550a.py

s = raw_input()
minAB = len(s) + 1
maxAB = -1
minBA = len(s) + 1
maxBA = -1

for i in range(len(s) - 1):
    if [s[i], s[i + 1]] == ['A', 'B']:
        minAB = i if i < minAB else minAB
        maxAB = i if i > maxAB else maxAB
    if [s[i], s[i + 1]] == ['B', 'A']:
        minBA = i if i < minBA else minBA
        maxBA = i if i > maxBA else maxBA

if maxBA - minAB > 1 or maxAB - minBA > 1:
    print 'YES'
else:
    print 'NO'