from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
# input = sys.stdin.readline

S = list(input())
S = [1-2*int(i=='B') for i in S]
T = list(accumulate([0]+S))
ans = 0
V = defaultdict(lambda:[])
for i,t in enumerate(T):
    V[t].append(i)
    
for v in V.values():
    ans = max(ans,v[-1]-v[0])
print(ans)