• محدودیت زمان: ۱ ثانیه
• محدودیت حافظه: ۲۵۶ مگابایت

One of the services that a reliable network provides is Jitter Minimization. Let me explain some more. In network communication, one node is sender and the other one is receiver. Also data is carried in units called packets. So, sender sends (data) packets to receiver.

Jitter Minimization: This service guarantees that the amount of time between the transmission of two successive packets at the sender is equal to the amount of time between their receipt at the destination.

Karen is a network administrator at Computer Science and Engineering Faculty in SBU. She wants to verify whether the network is reliable enough for Newbies2018 or not. So she sent $N$ packets from one node to another one, and wrote down the transmission and receive time for each packet on a single piece of paper. But, she forgot to write whether each entry was transmission time or receive time!!

Time to help, you are given a list of transmission and receive time of $N$ packets. Calculate how long did it take for each packet to reach the receiver (from sender), or state that the network isn’t reliable.

ورودی

The input file contains multiple test cases. (Number of tests doesn’t exceed $100$)

For each test case, first line contains a single integer $N$ – The number of packets. $$1 \leq N \leq 600$$

The second line consists of $2N$ distinct integers $t_i$ – the entries on Karen’s paper $$0 \leq t_i \leq 10^9$$

The input terminates with the $N = 0$, this case should not be processed.

خروجی

For each test case print the minimum possible time between send and receive of packets, or print Unreliable Network in a single line.

مثال‌ها

ورودی نمونه ۱

3
1 3 5 6 4 7
2
1 3 4 6
3
1 2 3 4 12 15
0

خروجی نمونه ۱

2
2
Unreliable Network

In the first test case:

• Packet $1$ is sent at $t = 1,$ and is received at $t = 3 \to$ Time between send and receive $= 2$
• Packet $2$ is sent at $t = 4,$ and is received at $t = 6 \to$ Time between send and receive $= 2$
• Packet $3$ is sent at $t = 5,$ and is received at $t = 7 \to$ Time between send and receive $= 2$

All transmission times are equal to $2,$ so network is reliable.