n=int(input())
a=0
for i in range(n):
    s=input().split()
    w=s[0].split(":")
    g=s[1].split(":")
    wh=int(w[0])
    wm=int(w[1])
    gh=int(g[0])
    gm=int(g[1])
    if wh>gh:
        gh=gh+24
    elif wh==gh and gm<wm:
        gh=gh+24
    a+=gh*60+gm-wh*60-wm
print(a)