n=int(input())
l=[]
for i in range(n):
	s,w=input().split()
	l+=[[s.split(':'),w.split(':')]]
t=0
for i in l:
	sh,sm=int(i[0][0]),int(i[0][1])
	wh,wm=int(i[1][0]),int(i[1][1])
	t+=(wh-sh)%24*60+(wm-sm)
print(t)