import sys


def input(): return sys.stdin.readline().rstrip()


def main():
    N = int(input())

    def cvt(x):
        a, b = x.split(':')
        return int(a)*60+int(b)

    ans = 0
    for i in range(N):
        HM, hm = input().split()
        ans += (cvt(hm)-cvt(HM)) % 1440

    print(ans)


if __name__ == '__main__':
    main()