S = input()
listS = list(S)
listN = []
listA = []
listMAX = []
count = 0
mx = 0
mn = 0
for a in listS:
    if a == "A":
        count += 1
        listN.append(count)
    if a == "B":
        count -= 1
        listN.append(count)
        
for b in listN:
    if listA.count(b) ==0:
        listA.append(b)
        
for c in listA:
    flag = 0
    for d,e in enumerate(listN):
        if str(e) == str(c) and flag ==0:
            min = int(d)
            flag = 1
        elif str(e) == str(c) and flag ==1:
            mx = int(d)
    listMAX.append(mx - mn)
  
print(max(listMAX))