func time2min(time: String) -> Int {
    let hm = time.split(separator: ":")
    let h = Int(hm[0])
    let m = Int(hm[1])
    return (h! * 60 + m!)
}

let N = Int(readLine()!)
var totalMinute = 0

for _ in 1...N!{
    let times = readLine()!.split(separator: " ")
    let time1 = String(times[0])
    let time2 = String(times[1])
    let minute1 = time2min(time: time1)
    let minute2 = time2min(time: time2)
    let sleepMinute = minute2 - minute1
    totalMinute += (sleepMinute + (sleepMinute < 0 ? 24 * 60 : 0))
}
print(totalMinute)