package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	var N, total, s, e, t int
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	N, _ = strconv.Atoi(sc.Text())
	for i := 0; i < N; i++ {
		sc.Scan()
		tokens := strings.Split(sc.Text(), " ")
		t, _ = strconv.Atoi(strings.Split(tokens[0], ":")[0])
		s = t * 60
		t, _ = strconv.Atoi(strings.Split(tokens[0], ":")[1])
		s += t
		t, _ = strconv.Atoi(strings.Split(tokens[1], ":")[0])
		e = t * 60
		t, _ = strconv.Atoi(strings.Split(tokens[1], ":")[1])
		e += t
		if e < s {
			e += 24 * 60
		}
		total += e - s
	}
	fmt.Println(total)
}