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

  if len(str(s_h)) == 2 and len(str(w_h)) <= 1:
    w_all = int(w_h) * 60 + 1440 + int(w_m)
    s_all = int(s_h) * 60 + int(s_m)
  elif s_h == 0 and w_h == 0 and s_m <= w_m:
    w_all = w_m - s_m
  elif s_h == 0 and w_h == 0 and s_m >= w_m:
    w_all = 1440 - s_m
  elif len(str(s_h)) <= 1 and len(str(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)