N = int(input())
ans = 0
for i in range(N) :
    A,B = input().split()
    ah,am = A.split(":")
    bh,bm = B.split(":")
    ah = int(ah)
    am = int(am)
    bh = int(bh)
    bm = int(bm)
    
    if ah > bh :
        bh += 24
    
    at = 60*ah + am
    bt = 60*bh + bm
    
    ans += bt - at

print(ans)