package main

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

var sc = bufio.NewScanner(os.Stdin)
var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func main() {
	sc.Split(bufio.ScanWords)
	n := nextInt()
	total := 0.0
	for i := 0; i < n; i++ {
		s, e := strings.Split(nextLine(), ":"), strings.Split(nextLine(), ":")
		var si, ei []int
		for _, v := range s {
			val, _ := strconv.Atoi(v)
			si = append(si, val)
		}
		for _, v := range e {
			val, _ := strconv.Atoi(v)
			ei = append(ei, val)
		}
		st, _ := time.Parse("15:04", fmt.Sprintf("%02d:%02d", si[0], si[1]))
		et, _ := time.Parse("15:04", fmt.Sprintf("%02d:%02d", ei[0], ei[1]))
		if ei[0] < si[0] || (ei[0] == si[0] && ei[0] <= si[0]) {
			et = et.Add(24 * time.Hour)
		}

		total += et.Sub(st).Minutes()
	}
	fmt.Println(int(total))
}

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	i, _ := strconv.Atoi(nextLine())
	return i
}

func nextInt64() int64 {
	i, _ := strconv.ParseInt(nextLine(), 10, 64)
	return i
}

func nextUint64() uint64 {
	i, _ := strconv.ParseUint(nextLine(), 10, 64)
	return i
}

func nextFloat() float64 {
	f, _ := strconv.ParseFloat(nextLine(), 64)
	return f
}

func readLine() string {
	buf := make([]byte, 0, 1000000)
	for {
		l, p, e := rdr.ReadLine()
		if e != nil {
			panic(e)
		}
		buf = append(buf, l...)
		if !p {
			break
		}
	}
	return string(buf)
}