N = int(input())
ans = 0
for i in range(N):
    neta, okita = input().split()
    j = neta.index(":")
    H = int(neta[:j])
    M = int(neta[j + 1:])
    j = okita.index(":")
    h = int(okita[:j])
    m = int(okita[j + 1:])
    if H > h:
        H -= 24
    if M > m:
        M -= 60
        H += 1
    ans += (h - H) * 60 + (m - M)
print(ans)