package main

import . "fmt"
import "time"

func main() {
	var n int
	Scan(&n)
	d:=0*time.Second
	const f="15:04"
	for ;n>0;n-- {
		var s,t string
		Scan(&s,&t)
		a,_:=time.Parse(f,s)
		b,_:=time.Parse(f,t)
		if b.Compare(a)<= 0 {
			b.AddDate(0,0,1)
		}
		d+=b.Sub(a)
	}
	Println(int64(d.Seconds()))
}