import sys import pypyjit import itertools import heapq import math from collections import deque, defaultdict import bisect input = sys.stdin.readline sys.setrecursionlimit(10 ** 6) pypyjit.set_param('max_unroll_recursion=-1') def index_lt(a, x): 'return largest index s.t. A[i] < x or -1 if it does not exist' return bisect.bisect_left(a, x) - 1 def index_le(a, x): 'return largest index s.t. A[i] <= x or -1 if it does not exist' return bisect.bisect_right(a, x) - 1 def index_gt(a, x): 'return smallest index s.t. A[i] > x or len(a) if it does not exist' return bisect.bisect_right(a, x) def index_ge(a, x): 'return smallest index s.t. A[i] >= x or len(a) if it does not exist' return bisect.bisect_left(a, x) T = input()[:-1] A = [1 if c == 'A' else -1 for c in T] S = [0] * (len(T) + 1) for i in range(len(T)): S[i + 1] = S[i] + A[i] D = defaultdict(list) for i in range(len(S)): D[S[i]].append(i) ans = 0 for vs in D.values(): ans = max(ans, vs[-1] - vs[0]) print(ans)