N=int(input())
T=[[i for i in input (). split()] for i in range (N)]
H=[[0]*4]*N
#H=[0]*N
#M=[0]*N
#=[0]*N
#M=[0]*N
S=0
for i in range (N):
  #  print (T[i][0])
    H[i][0],H[i][1]=(T[i][0]. split (":"))
    H[i][2],H[i][3]=(T[i][1]. split (":"))
    for j in range(4):
        H[i][j]=int(H[i][j])
    M=H[i][3]-H[i][1]
  #  if M<0:
    #    M+=60
     #   H[i][0]-=1
    Hh=H[i][2]-H[i][0]
    if Hh<0:
        Hh+=24
    Hh*=60
    Hh+=M
    S+=Hh
  #  print (S)
print (S)