// No.70 睡眠の重要性！
package main

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

func main() {
	var n int
	fmt.Scan(&n)

	type Sleep struct {
		Gbed string
		Wake string
	}
	rec := make([]Sleep, n)
	for i := 0; i < n; i++ {
		fmt.Scan(&rec[i].Gbed, &rec[i].Wake)
	}

	var hh, mm string
	var h1, h2, m1, m2 int
	var ans float64
	for _, r := range rec {
		hh, mm, _ = strings.Cut(r.Gbed, ":")
		h1, _ = strconv.Atoi(hh)
		m1, _ = strconv.Atoi(mm)

		hh, mm, _ = strings.Cut(r.Wake, ":")
		h2, _ = strconv.Atoi(hh)
		m2, _ = strconv.Atoi(mm)

		gt := time.Date(1, 1, 1, h1, m1, 0, 0, time.Now().Location())
		wt := time.Date(1, 1, 1, h2, m2, 0, 0, time.Now().Location())
		if gt.After(wt) {
			wt = wt.AddDate(0, 0, 1)
		}
		ans += wt.Sub(gt).Minutes()
	}
	fmt.Println(ans)
}