n = int(input())

time = 0
for i in range(n):
    bed_in, bed_out = input().split(' ')
    
    h, m = map(int, bed_in.split(':'))
    bed_in = 60 * h + m
    
    h, m = map(int, bed_out.split(':'))
    bed_out = 60 * h + m
    
    time += bed_out - bed_in if bed_in <= bed_out else 1440 - (bed_in - bed_out)

print(time)