use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let mut a = s.lines().last().unwrap().to_owned();
	let mut b = 0;
	a.push_str("A");
	println!(
		"{}",
		(0..a.len() - 2)
			.filter(|&i| match &a[i..i + 3] {
				"BAB" => false,
				"BBA" | "BBB" => {
					b = 1;
					false
				}
				_ => true,
			})
			.count() + b
	)
}