n = int(input())
ret = 0
for _ in range(n):
    line = list(input().split())
    h1,m1 = map(int, line[0].split(':'))
    h2,m2 = map(int, line[1].split(':'))
    s = h2*60+m2 - h1*60-m1
    if s<0:
        s += 24*60
    ret += s
print(ret)