S = str(input())
N = len(S)
stack = []
ans = 1
for i in range(N):
  if not stack:
    stack.append(S[i])
    ans += 1
  else:
    if stack[-1] == S[i]:
      stack.pop()
    else:
      stack.append(S[i])
      ans += 1
print(ans)