#![allow(non_snake_case)] #[allow(unused_macros)] macro_rules! input { (source = $s:expr, $($r:tt)*) => { let mut tokens = $s.split_whitespace(); input_inner! { tokens, $($r)* } }; ($($r:tt)*) => { let s = { use std::io::Read; let mut res = String::new(); ::std::io::stdin().read_to_string(&mut res).unwrap(); res }; let mut tokens = s.split_whitespace(); input_inner! { tokens, $($r)* } }; } #[allow(unused_macros)] macro_rules! input_inner { ($tokens:expr) => {}; ($tokens:expr,) => {}; ($tokens:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($tokens, $t); input_inner! { $tokens $($r)* } }; } #[allow(unused_macros)] macro_rules! read_value { ($tokens:expr, ( $($t:tt),* )) => { ( $(read_value!($tokens, $t)),* ) }; ($tokens:expr, [ $t:tt; $len:expr ]) => { (0..$len).map(|_| read_value!($tokens, $t)).collect::>() }; ($tokens:expr, chars) => { read_value!($tokens, String).chars().collect::>() }; ($tokens:expr, usize1) => { read_value!($tokens, usize) - 1 }; ($tokens:expr, $t:ty) => { $tokens.next().unwrap().parse::<$t>().expect("parse error") }; } use std::collections::{ HashMap }; fn chmax(xmax: &mut T, x: T) -> bool where T: PartialOrd + Copy { if *xmax < x { *xmax = x; true } else { false } } fn main() { input! { S: chars, } let mut lefts = HashMap::::new(); lefts.insert(0, 0); let mut ans = 0; let mut h = 0; for (i,c) in S.into_iter().enumerate() { match c { 'A' => { h += 1; }, 'B' => { h -= 1; }, _ => { panic!(); }, } let l = *lefts.entry(h).or_insert(i); chmax(&mut ans, i-l); } println!("{}", ans); }