fun main(arr:Array<String>) {
    val dayCount = readLine()!!.toInt()
    val ans = (1..dayCount).map { readLine()!!.split(" ").map { it.split(":").map { it.toInt() }.let { it[0]*60+it[1] } }.let { it[1] - it[0] } }.map { if (it >= 0) it else it+(60*24) }
    println(ans.sum())
}