Middle Element or Sum of Middle Elements

Given a positive integer \( n \), construct a sequence \( a \) of length \( n \) such that \( a_i=i \) for \( 1\le i\le n \).

If \( n \) is odd, output the middle element of \( a \) (i.e. the element at position \( \frac{n+1}{2} \)). Otherwise, if \( n \) is even, output the sum of the two middle elements (i.e. the sum of the elements at positions \( \frac{n}{2} \) and \( \frac{n}{2}+1 \)).

inputFormat

The input contains a single positive integer \( n \) (\( n \ge 1 \)).

outputFormat

Output a single integer which is either the middle element of the sequence if \( n \) is odd, or the sum of the two middle elements if \( n \) is even.

sample

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