impl Solution {
    pub fn find_nth_digit(mut n: i32) -> i32 {
        let mut m = n as i64;
        let mut i = 1;
        let mut k = 1;
        while m > 9 * k * i {
            m -= 9 * i * k;
            i += 1;
            k *= 10;
        }
        let y = (m - 1) % i;
        let x = (m - 1) / i;
        let target_num = k + x;
        let s = target_num.to_string();
        let result = s.chars().nth(y as usize).unwrap().to_digit(10).unwrap();
        return result as i32;
    }
}