use std::io::*;
use std::str::FromStr;

#[allow(dead_code)]
fn get_line() -> String {
    let stdin = stdin();
    let mut line = String::new();
    stdin.lock().read_line(&mut line).expect("io error.");
    line.trim().to_string()
}

#[allow(dead_code)]
fn get_word<T: FromStr>() -> T {
    (&get_line()).parse().ok().expect("parse error.")
}

#[allow(dead_code)]
fn get_vec<T: FromStr>() -> Vec<T> {
    (&get_line()).split(' ').map(|x| x.parse().ok().expect("parse error.")).collect()
}

fn main() {
    let n = get_word::<u64>();

    let mut ans = 0;
    for _ in 0..n {
        let v = get_vec::<String>();
        let mut t = to_min(&v[1]) - to_min(&v[0]);
        if t < 0 {
            t += 1440;
        }
        ans += t;
    }

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

fn to_min(s: &String) -> i64 {
    let t: Vec<i64> = s.split(':')
                .map(|x| x.parse().ok().unwrap())
                .collect();
    t[0] * 60 + t[1]
}