/// chmax, chmin sugar syntax
pub trait Change {
    fn chmax(&mut self, x: Self) -> bool;
    fn chmin(&mut self, x: Self) -> bool;
}
impl<T: PartialOrd> Change for T {
    fn chmax(&mut self, x: T) -> bool {
        if *self < x {
            *self = x;
            true
        } else {
            false
        }
    }
    fn chmin(&mut self, x: T) -> bool {
        if *self > x {
            *self = x;
            true
        } else {
            false
        }
    }
}