https://atcoder.jp/contests/math-and-algorithm/tasks/panasonic2020_b
HWが偶数と奇数で変わりますが、HかWが1のときは身動きが取れないので特殊ですね。
// Bishop #![allow(non_snake_case)] //////////////////// library //////////////////// fn read<T: std::str::FromStr>() -> T { let mut line = String::new(); std::io::stdin().read_line(&mut line).ok(); line.trim().parse().ok().unwrap() } fn read_vec<T: std::str::FromStr>() -> Vec<T> { read::<String>().split_whitespace() .map(|e| e.parse().ok().unwrap()).collect() } //////////////////// process //////////////////// fn read_input() -> (usize, usize) { let v = read_vec(); let H = v[0]; let W = v[1]; (H, W) } fn f(H: usize, W: usize) -> usize { if H == 1 || W == 1 { 1 } else { (H * W + 1) / 2 } } fn main() { let (H, W) = read_input(); println!("{}", f(H, W)) }