import sys
import math as mas

n=int(input())
sum=0
for i in range(n):
	s=input()
	a,b=map(str,s.split())
	c=list(map(int,a.split(':')))
	fro=c[0]*60+c[1]
	c=list(map(int,b.split(':')))
	to=c[0]*60+c[1]
	if fro<to:sum+=to-fro
	else:sum+=24*60-fro+to
print(sum)

#for i in sys.stdin:
#	a,b=map(int,i.split())
#	print(gcd(a,b),lcm(a,b))