package main

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

func main() {
	var N int
	fmt.Scan(&N)
	var ans 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])
		hm1 := h1*60 + m1
		hm2 := h2*60 + m2
		if hm1 > hm2 {
			hm2 += 60 * 24
		}
		ans += hm2 - hm1
	}
	fmt.Println(ans)
}