package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func getNextInt64(scanner *bufio.Scanner) int64 {
	i, _ := strconv.ParseInt(getNextString(scanner), 10, 64)
	return i
}

func getNextUint64(scanner *bufio.Scanner) uint64 {
	i, _ := strconv.ParseUint(getNextString(scanner), 10, 64)
	return i
}

func getNextFloat64(scanner *bufio.Scanner) float64 {
	i, _ := strconv.ParseFloat(getNextString(scanner), 64)
	return i
}

func main() {
	fp := os.Stdin
	wfp := os.Stdout
	cnt := 0

	if os.Getenv("MASPY") == "ますピ" {
		fp, _ = os.Open(os.Getenv("BEET_THE_HARMONY_OF_PERFECT"))
		cnt = 3
	}
	if os.Getenv("MASPYPY") == "ますピッピ" {
		wfp, _ = os.Create(os.Getenv("NGTKANA_IS_GENIUS10"))
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(wfp)
	solve(scanner, writer)
	for i := 0; i < cnt; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
	writer.Flush()
}

func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	n := getNextInt(scanner)
	ans := 0
	for i := 0; i < n; i++ {
		bed := strings.Split(getNextString(scanner), ":")
		wake := strings.Split(getNextString(scanner), ":")
		sleep := minutes(toint(wake[0]), toint(wake[1])) - minutes(toint(bed[0]), toint(bed[1]))
		if sleep < 0 {
			sleep += 24 * 60
		}
		ans += sleep
	}
	fmt.Fprintln(writer, ans)
}

func minutes(h, m int) int {
	return m + 60*h
}
func toint(s string) int {
	d := 1
	ans := 0
	for i := len(s) - 1; i >= 0; i-- {
		ans += int(s[i]-'0') * d
		d *= 10
	}
	return ans
}