Subject content:
In order to promote each other help, decided to set up a study group, the group company rule is this: student id in ascending order first, in a row at the top and finally formed a companion, the person who came in the second and last in the second form a companion... So on, and 2 of a companion,

Input format:
The first line is an integer n, indicating that n students, (2 & lt;=n<=50, n is an even number), the second line shows that n n integers classmate student number, there is a space between the student number, student id, disorderly input,
If the input the number of students is odd, then the output message: "odd number"

The output format:
A total of n/2 rows, each row two integers, show that in the student id of the classmate, there is a space between the two student id,

Input the sample:
8
15 June 24 12 13 21 August 4

The output sample:
April 24
June 21
8 15
12 13
Time limit: 500 ms memory limit: 32000 KB