N = input()
List,X =[],[]
for i in range(0,N):
    w_split = raw_input().split()
    A,B = w_split[0],w_split[1]
    a,b = A.split(':')
    c,d = B.split(':')
    if int(a) >= int(c):
        x=(24-(int(a)+1))*60+(60-int(b))+int(c)*60+int(d)
    else:
        x=(int(c)-int(a))*60+(int(d)-int(b))
    X.append(x)
print sum(X)