package main

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

func main() {
	var n int
	fmt.Scan(&n)
	ans := 0
	for range make([]struct{}, n) {
		t := 0
		for i := 0; i < 2; i++ {
			var s string
			fmt.Scan(&s)
			t += f(s, i)
		}
		if t < 0 {
			t += 24 * 60
		}
		ans += t
	}
	fmt.Println(ans)
}

func f(s string, i int) (res int) {
	a := strings.Split(s, ":")
	a0, _ := strconv.Atoi(a[0])
	a1, _ := strconv.Atoi(a[1])
	res = a0*60 + a1
	if i == 0 {
		res *= -1
	}
	return
}