import strutils, sequtils
let N = stdin.readline.parseInt
var ttl = 0

for j in 0 ..< N:
  let HMHM = stdin.readLine.split
  var sb_ttl = 0
  for i, HM in HMHM:
    let hm = HM.split(':').map parseInt
    let sgn = [-1, 1][int(i == 1)]
    sb_ttl += sgn * (60 * hm[0] + hm[1])
  sb_ttl = (sb_ttl + 24 * 60) mod (24 * 60)
  ttl += sb_ttl
echo ttl