import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def MI(): return map(int, sys.stdin.readline().split())
def MI1(): return map(int1, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

def main():
    n = int(input())
    ans = 0
    for _ in range(n):
        hm0, hm1 = input().split()
        h0, m0 = map(int, hm0.split(":"))
        h1, m1 = map(int, hm1.split(":"))
        if m1 < m0:
            m1 += 60
            h1 -= 1
        if h1 < h0: h1 += 24
        ans += 60 * (h1 - h0) + (m1 - m0)
    print(ans)

main()