n = int(input())
total = 0
for i in range(n):
  s, w = input().split()
  s_h, s_m= s.split(':')
  w_h, w_m= w.split(':') 

  if len(s_h) == 2 and len(w_h) <= 1:
    w_all = int(w_h) * 60 + 1440 + int(w_m)
    s_all = int(s_h) * 60 + int(s_m)
  elif len(s_h) <= 1 and len(w_h) <= 1:
    w_all = int(w_h) * 60 + 1440 + int(w_m)
    s_all = int(s_h) * 60 + 1440 + int(s_m)
  total += w_all - s_all

print(total)