use std::collections::HashMap; fn main() { let s = input_line_str().to_charvec(); let mut h = HashMap::new(); let mut sum = 0_isize; let mut ans = 0; h.insert(0, 0); for (i, &c) in s.iter().enumerate() { if c == 'A' { sum += 1; } else { sum -= 1; } if h.contains_key(&sum) { ans = std::cmp::max(ans, i as isize - h[&sum]); } else { h.insert(sum, i as isize); } } //dbg!(&h); println!("{}", ans); } //https://github.com/manta1130/competitive-template-rs use input::*; pub mod input { use std::cell::RefCell; use std::io; pub const SPLIT_DELIMITER: char = ' '; pub use std::io::prelude::*; #[macro_export] thread_local! { pub static INPUT_BUFFER:RefCell>=RefCell::new(std::collections::VecDeque::new()); } #[macro_export] macro_rules! input_internal { ($x:ident : $t:ty) => { INPUT_BUFFER.with(|p| { if p.borrow().len() == 0 { let temp_str = input_line_str(); let mut split_result_iter = temp_str .split(SPLIT_DELIMITER) .map(|q| q.to_string()) .collect::>(); p.borrow_mut().append(&mut split_result_iter) } }); let mut buf_split_result = String::new(); INPUT_BUFFER.with(|p| buf_split_result = p.borrow_mut().pop_front().unwrap()); let $x: $t = buf_split_result.parse().unwrap(); }; (mut $x:ident : $t:ty) => { INPUT_BUFFER.with(|p| { if p.borrow().len() == 0 { let temp_str = input_line_str(); let mut split_result_iter = temp_str .split(SPLIT_DELIMITER) .map(|q| q.to_string()) .collect::>(); p.borrow_mut().append(&mut split_result_iter) } }); let mut buf_split_result = String::new(); INPUT_BUFFER.with(|p| buf_split_result = p.borrow_mut().pop_front().unwrap()); let mut $x: $t = buf_split_result.parse().unwrap(); }; } #[macro_export] macro_rules! inputv { ($i:ident : $t:ty) => { input_internal!{$i : $t} }; (mut $i:ident : $t:ty) => { input_internal!{mut $i : $t} }; ($i:ident : $t:ty $(,)*) => { input_internal!{$i : $t} }; (mut $i:ident : $t:ty $(,)*) => { input_internal!{mut $i : $t} }; (mut $i:ident : $t:ty,$($q:tt)*) => { input_internal!{mut $i : $t} inputv!{$($q)*} }; ($i:ident : $t:ty,$($q:tt)*) => { input_internal!{$i : $t} inputv!{$($q)*} }; } pub fn input_all() { INPUT_BUFFER.with(|p| { if p.borrow().len() == 0 { let mut temp_str = String::new(); std::io::stdin().read_to_string(&mut temp_str).unwrap(); let mut split_result_iter = temp_str .split_whitespace() .map(|q| q.to_string()) .collect::>(); p.borrow_mut().append(&mut split_result_iter) } }); } pub fn input_line_str() -> String { let mut s = String::new(); io::stdin().read_line(&mut s).unwrap(); s.trim().to_string() } #[allow(clippy::match_wild_err_arm)] pub fn input_vector() -> Vec where T: std::str::FromStr, { let mut v: Vec = Vec::new(); let s = input_line_str(); let split_result = s.split(SPLIT_DELIMITER); for z in split_result { let buf = match z.parse() { Ok(r) => r, Err(_) => panic!("Parse Error",), }; v.push(buf); } v } #[allow(clippy::match_wild_err_arm)] pub fn input_vector_row(n: usize) -> Vec where T: std::str::FromStr, { let mut v = Vec::with_capacity(n); for _ in 0..n { let buf = match input_line_str().parse() { Ok(r) => r, Err(_) => panic!("Parse Error",), }; v.push(buf); } v } pub trait ToCharVec { fn to_charvec(&self) -> Vec; } impl ToCharVec for String { fn to_charvec(&self) -> Vec { self.to_string().chars().collect::>() } } }