fn main() {
    input! {
        n: usize,
        times: [(String, String); n],
    }

    let mut ans = 0;

    for (bed, awake) in times {
        let bed = bed
            .split(':')
            .map(|x| x.parse::<usize>().unwrap())
            .collect::<Vec<usize>>();
        let awake = awake
            .split(':')
            .map(|x| x.parse::<usize>().unwrap())
            .collect::<Vec<usize>>();

        let bed_h = bed[0];
        let bed_m = bed[1];
        let awake_h = awake[0];
        let awake_m = awake[1];

        ans += (24 + awake_h - bed_h) % 24 * 60 + awake_m - bed_m;
    }

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

#[macro_export]
macro_rules! input{
    (sc=$sc:expr,$($r:tt)*)=>{
        input_inner!{$sc,$($r)*}
    };
    ($($r:tt)*)=>{
        let mut sc=self::Scanner::new(std::io::stdin().lock());
        input_inner!{sc,$($r)*}
    };
}

#[macro_export]
macro_rules! input_inner{
    ($sc:expr)=>{};
    ($sc:expr,)=>{};
    ($sc:expr,$var:ident:$t:tt$($r:tt)*)=>{
        let $var=read_value!($sc,$t);
        input_inner!{$sc $($r)*}
    };
}

#[macro_export]
macro_rules! read_value{
    ($sc:expr,($($t:tt),*))=>{
        ($(read_value!($sc,$t)),*)
    };
    ($sc:expr,[$t:tt;$len:expr])=>{
        (0..$len).map(|_|read_value!($sc,$t)).collect::<Vec<_>>()
    };
    ($sc:expr,Chars)=>{read_value!($sc,String).chars().collect::<Vec<char>>()};
    ($sc:expr,Usize1)=>{read_value!($sc,usize)-1};
    ($sc:expr,$t:ty)=>{$sc.nextsc::<$t>()};
}
pub struct Scanner {
    s: Box<str>,
    input: std::iter::Peekable<std::str::SplitAsciiWhitespace<'static>>,
}
impl Scanner {
    pub fn new<R: std::io::Read>(mut reader: R) -> Self {
        let s = {
            let mut s = String::new();
            reader.read_to_string(&mut s).unwrap();
            s.into_boxed_str()
        };
        let mut sc = Scanner {
            s,
            input: "".split_ascii_whitespace().peekable(),
        };
        use std::mem;
        let s: &'static str = unsafe { mem::transmute(&*sc.s) };
        sc.input = s.split_ascii_whitespace().peekable();
        sc
    }
    #[inline]
    pub fn nextsc<T: std::str::FromStr>(&mut self) -> T
    where
        T::Err: std::fmt::Debug,
    {
        self.input
            .next()
            .unwrap()
            .parse::<T>()
            .expect("Parse error")
    }
}