fun main(args: Array<String>)
{
    val n = readLine()!!.toInt()
    var sum = 0
    repeat(n) {
        var hm: List<Int> = readLine()!!.split(" ", ":").map { it.toInt() }
        if (hm[0] > hm[2]) sum += 24 * 60
        sum += hm[2] * 60 + hm[3] - hm[0] * 60 - hm[1]
    }
    println("${sum}")
}