# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N = int(input())
	ans = 0
	for i in range(N):
		A, B = list(input().split())
		H1, M1 = list(A.split(":"))
		h1, m1 = list(B.split(":"))
		H1 = int(H1); M1 = int(M1); h1 = int(h1); m1 = int(m1)
		dif = (60 * h1 + m1 - 60 * H1 - M1) % 1440
		ans += dif

	print(ans)


if __name__ == '__main__':
	main()