1006 Sign In and Sign Out (25)（25 分）

At the beginning of every day, the first person who signs in the

computer room will unlock the door, and the last one who signs out will

lock the door. Given the records of signing in's and out's, you are

supposed to find the ones who have unlocked and locked the door on that

day.

Input Specification:

Each input file contains one test case. Each case contains the records

for one day. The case starts with a positive integer M, which is the

total number of records, followed by M lines, each in the format:

ID_number Sign_in_time Sign_out_time

where times are given in the format HH:MM:SS, and ID number is a string

with no more than 15 characters.

Output Specification:

For each test case, output in one line the ID numbers of the persons who

have unlocked and locked the door on that day. The two ID numbers must

be separated by one space.

Note: It is guaranteed that the records are consistent. That is, the

sign in time must be earlier than the sign out time for each person, and

there are no two persons sign in or out at the same moment.

Sample Input:

3

CS301111 15:30:28 17:00:10

SC3021234 08:00:00 11:25:25

CS301133 21:45:00 21:58:40

Sample Output:

SC3021234 CS301133