h=int()
m=int()

for i in range(int(input())):
    n,l=input().split()
    h1,m1=(int(i) for i in n.split(":"))
    h2,m2=(int(i) for i in l.split(":"))
   
    if int(h2)<int(h1):
        h=int(h)+int(h2)+int(24)-int(h1)
    else:
        h=int(h)+int(h2)-int(h1)
    if m2<m1:
        m=int(m)+int(m2)+int(60)-int(m1)
        h=h-1
    else:
        m=int(m)+int(m2)-int(m1)
    i=i+1

if h==-1:
    h=23
   
print(h*60+m)