#![allow(dead_code, unused_variables, unused_macros)] fn main() { input!(n:i32,k:i32); let ans = match k { _ if k - 1 == n - k => n - 1, _ if (1..=n).contains(&k) => n - 2, _ => 0, }; println!("{ans}"); } mod xxx { // https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 #[macro_export] macro_rules! input { (source = $s:expr, $($r:tt)*) => { input_inner!{$s, $($r)*} }; ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes .by_ref() .map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } #[macro_export] macro_rules! input_inner { ($next:expr) => {}; ($next:expr, ) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } #[macro_export] macro_rules! read_value { ($next:expr, ( $($t:tt),* )) => { ( $(read_value!($next, $t)),* ) }; ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, chars) => { read_value!($next, String).chars().collect::>() }; ($next:expr, usize1) => { read_value!($next, usize) - 1 }; ($next:expr, bits)=>{ u64::from_str_radix(&$next(), 2).expect("Parse error") }; ($next:expr, hexs)=>{ u64::from_str_radix(&$next(), 16).expect("Parse error") }; ($next:expr, $t:ty) => { $next().parse::<$t>().expect("Parse error") }; } }