fun main(args:Array<String>) {
  val inputs = readLine()!!.toList().map {
    when {
      it == 'A' -> 1
      else -> -1
    }
  }
  // scanner
  var s = 0
  val tri = mutableListOf<Int>(0)
  inputs.map {
    s += it
    tri.add(s)
  }
  val pats = tri.toSet()
  val ans = mutableListOf<Int>()
  pats.map { pat ->
    var start = -1
    for( _start in (0..tri.size-1) ) {
      if( tri[_start] == pat ) {
        start = _start
        break
      }
    }
    var end = -1
    for( _end in (tri.size-1 downTo 0) ) {
      if( tri[_end] == pat ) {
        end = _end
        break
      }
    }
    ans.add( end - start )
  }
  ans.max()?.let(::println) ?: println(0)
}