package main

import (
	"fmt"
)

func main() {
	var N, ans int
	fmt.Scan(&N)
	var h1, m1, h2, m2, t1, t2 int
	for i:=0;i<N;i++{
		fmt.Scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2)
		t1 = h1*60+m1
		t2 = h2*60+m2
		t := t2 - t1
		if t < 0{
			t = 24*60+t
		}
		ans += t
	}
	fmt.Println(ans)
}