pub fn main() {
    let v = vec![
        (1, 31),
        (2, 28),
        (3, 31),
        (4, 30),
        (5, 31),
        (6, 30),
        (7, 31),
        (8, 31),
        (9, 30),
        (10, 31),
        (11, 30),
        (12, 31),
    ];
    let all_date: Vec<(usize, usize)> = v.iter()
        .flat_map(|&(m, d)| (1..d).map(move |x| (m, x)))
        .collect();
    let sum_digit = |x| (x / 10) + (x % 10);

    let mut count = 0;
    for (m, d) in all_date {
        if m == sum_digit(d) {
            count += 1;
        }
    }
    println!("{}", count);
}