N = int(input())
ans = 0
for i in range(N) :
    a,b = input().split()
    ha,ma = map(int,a.split(":"))
    hb,mb = map(int,b.split(":"))
    c = 0
    if ha > hb or (ha == hb and ma > mb) :
        c += ((24-ha)+hb)*60
    else :
        c += (hb-ha)*60
    if ma >= mb :
        c -= (ma-mb)
    else :
        c += (mb-ma)
    ans += c
print(ans)