package main

import (
	"fmt"
	"strconv"
	"strings"
)

func main() {
	var N int
	fmt.Scan(&N)
	var h, m int
	for i := 0; i < N; i++ {
		var s1, s2 string
		fmt.Scan(&s1, &s2)
		h1, _ := strconv.Atoi(strings.Split(s1, ":")[0])
		m1, _ := strconv.Atoi(strings.Split(s1, ":")[1])
		h2, _ := strconv.Atoi(strings.Split(s2, ":")[0])
		m2, _ := strconv.Atoi(strings.Split(s2, ":")[1])
		// 23:59 -> 05:41 => 05:42
		// h1:m1 -> h2:m2
		if m1 > m2 {
			h2--
			if h2 < 0 {
				h2 += 24
			}
			m2 += 60
		}
		m += m2 - m1
		if h1 > h2 {
			h2 += 24
		}
		h += h2 - h1
	}
	fmt.Println(h*60 + m)
}