class Problem0070:
	def solve(this):
		n = int(input())
		
		res = 0
		for i in range(n):
			s,e = input().split()
			
			s1,s2 = map(int, s.split(":"))
			e1,e2 = map(int, e.split(":"))
			sm = s1 * 60 + s2
			em = e1 * 60 + e2
			if sm > em:
				res += (24*60 - sm) + em
			else:
				res += em - sm
		print(res)

if __name__ == "__main__":
	problem = Problem0070()
	problem.solve()