n=int(input())
x=0
y=0
for i in range(0,n):
    a=input()
    b=a.split()
    c,d=map(int,b[0].split(':'))
    e,f=map(int,b[1].split(':'))
    if c<=e:
        g=e-c
        x+=g
    elif c>e:
        g=e-0
        g+=(24-c)
        x+=g
    if d<=f:
        h=f-d
        y+=h
    elif d>f:
        h=f-0
        h+=(60-d)
        x-=1
        y+=h
z=x*60+y
print(z)