package main

import "fmt"

func main() {
	var n, h1, m1, h2, m2 int
	_, _ = fmt.Scan(&n)

	total := 0
	for i := 0; i < n; i++ {
		_, _ = fmt.Scanf("%d:%d", &h1, &m1)
		_, _ = fmt.Scanf("%d:%d", &h2, &m2)

		t1 := h1*60 + m1
		t2 := h2*60 + m2
		total += (t2 + 24*60 - t1) % (24 * 60)
	}

	fmt.Println(total)
}