单点时限: 2.0 sec
内存限制: 256 MB
Input two integers $a$ and $b$ of type int, and output average integer of $a$ and $b$.
Note: $a$ and $b$ may be very large, like $2147483647$.
If the average is not an integer, you should output the nearest integer which is, at the same time, closer to $0$.
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