https://atcoder.jp/contests/math-and-algorithm/tasks/math_and_algorithm_az
4の剰余を取るだけですね。
// Stones Game 1 #![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() } //////////////////// process //////////////////// fn f(N: u64) { if N % 4 != 0 { println!("First") } else { println!("Second") } } fn main() { let N = read(); f(N) }