n = int(input())
e = [[i for i in input().split()] for i in range(n)]
s = 0
for ee in e:
  a = int(ee[0].split(':')[0])
  b = int(ee[0].split(':')[1])
  c = int(ee[1].split(':')[0])
  d = int(ee[1].split(':')[1])
  s += ((24 + c - a) * 60 + d - b) % (24 * 60)
print(s)