fn main() {
    let mut input = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut input).ok();
    let input: Vec<i64> = input
        .split(['\n', ' ', ':'])
        .skip(1)
        .flat_map(str::parse)
        .collect();

    let mut answer = 0;

    for i in (0..input.len()).step_by(4) {
        if let &[h1, m1, h2, m2] = &input[i..i + 4] {
            let mut duration = 60 * (h2 - h1) + (m2 - m1);
            if duration < 0 {
                duration += 24 * 60;
            }

            answer += duration;
        }
    }

    println!("{}", answer);
}