N = int(input())
T = []
for i in range(N):
    bd, up = map(str, input().split())
    bd = bd.split(':')
    up = up.split(':')
    time = [bd, up]
    T.append(time)

slptm = 0
for i in range(N):
    t0_i = int(T[i][0][0]) 
    t1_i = int(T[i][0][1])
    t2_i = int(T[i][1][0])
    t3_i = int(T[i][1][1])
    
    bd_m = 60*t0_i + t1_i
    up_m = 60*t2_i + t3_i

    if bd_m > up_m:
        slp = up_m + (24*60 - bd_m)
        slptm += slp
    else:
        slp = up_m - bd_m
        slptm += slp

print(slptm)