package main

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

func main() {
	sc := NewScanner(os.Stdin)
	N, _ := sc.NextInt()
	var sum int = 0
	for i := 1; i <= N; i++ {
		s, _ := sc.Next()
		e, _ := sc.Next()
		start := strings.Split(s, ":")
		end := strings.Split(e, ":")
		sh, _ := strconv.Atoi(start[0])
		sm, _ := strconv.Atoi(start[1])
		eh, _ := strconv.Atoi(end[0])
		em, _ := strconv.Atoi(end[1])
		dh, dm := eh-sh, em-sm
		if dm < 0 {
			dm += 60
			dh--
		}
		sum += dm
		if dh < 0 {
			dh += 24
		}
		sum += dh * 60
	}
	fmt.Println(sum)
}

type Scanner struct {
	*bufio.Scanner
}

func NewScanner(r io.Reader) *Scanner {
	return &Scanner{
		bufio.NewScanner(r),
	}
}

func (s *Scanner) Next() (string, error) {
	s.Scanner.Split(bufio.ScanWords)
	return s.nextToken()
}

func (s *Scanner) nextToken() (string, error) {
	sc := s.Scanner
	if sc.Scan() {
		return sc.Text(), nil
	}
	if sc.Err() != nil {
		return "", sc.Err()
	}
	return "", io.EOF
}

func (s *Scanner) NextInt() (int, error) {
	token, err := s.Next()
	if err != nil {
		return 0, err
	}
	return strconv.Atoi(token)
}