fn main() { input! { n: isize, k: isize } let d = n - k; println!("{}", if d >= 0 { 2isize.pow(d as u32) } else { 0 }); } #[macro_export] macro_rules! input{ (sc=$sc:expr,$($r:tt)*)=>{ input_inner!{$sc,$($r)*} }; ($($r:tt)*)=>{ let mut sc=self::Scanner::new(std::io::stdin().lock()); input_inner!{sc,$($r)*} }; } #[macro_export] macro_rules! input_inner{ ($sc:expr)=>{}; ($sc:expr,)=>{}; ($sc:expr,$var:ident:$t:tt$($r:tt)*)=>{ let $var=read_value!($sc,$t); input_inner!{$sc $($r)*} }; } #[macro_export] macro_rules! read_value{ ($sc:expr,($($t:tt),*))=>{ ($(read_value!($sc,$t)),*) }; ($sc:expr,[$t:tt;$len:expr])=>{ (0..$len).map(|_|read_value!($sc,$t)).collect::>() }; ($sc:expr,Chars)=>{read_value!($sc,String).chars().collect::>()}; ($sc:expr,Usize1)=>{read_value!($sc,usize)-1}; ($sc:expr,$t:ty)=>{$sc.nextsc::<$t>()}; } pub struct Scanner { s: Box, input: std::iter::Peekable>, } impl Scanner { pub fn new(mut reader: R) -> Self { let s = { let mut s = String::new(); reader.read_to_string(&mut s).unwrap(); s.into_boxed_str() }; let mut sc = Scanner { s, input: "".split_ascii_whitespace().peekable(), }; use std::mem; let s: &'static str = unsafe { mem::transmute(&*sc.s) }; sc.input = s.split_ascii_whitespace().peekable(); sc } #[inline] pub fn nextsc(&mut self) -> T where T::Err: std::fmt::Debug, { self.input .next() .unwrap_or_default() .parse::() .expect("Parse error") } }