N = int(input())
L = [list(map(int,str(input()).replace(':',' ').split())) for x in range(N)]
S = 0
for n in range(N):
    if L[n][0] <= L[n][2]:
        S += (L[n][2]-L[n][0])*60
    else:
        S += (24 + L[n][2]-L[n][0])*60

for n in range(N):
    S += L[n][3] - L[n][1]

print(S)