package main

import (
	"fmt"
)

type Date struct {
	Hour   int
	Minute int
}

func resolve(N int, H, h []Date) int {
	ret := 0
	for i := 0; i < N; i++ {
		if (H[i].Hour > h[i].Hour) || (H[i].Hour == h[i].Hour && H[i].Minute > h[i].Minute) {
			ret += (23 - H[i].Hour) * 60
			ret += 60 - H[i].Minute
			H[i] = Date{0, 0}
		}
		ret += (h[i].Hour - H[i].Hour) * 60
		ret += h[i].Minute - H[i].Minute
	}
	return ret
}

func main() {
	var N int
	fmt.Scanf("%d\n", &N)
	H := make([]Date, N)
	h := make([]Date, N)
	for i := 0; i < N; i++ {
		fmt.Scanf("%d:%d", &H[i].Hour, &H[i].Minute)
		fmt.Scanf("%d:%d\n", &h[i].Hour, &h[i].Minute)
	}
	fmt.Println(resolve(N, H, h))
}