Giải bài trực tuyến

The Recaman’s sequence is defined by a0 = 0 ; for m > 0, a(m) = a(m−1) − m if the resulting a(m) is positive and not already in the sequence, otherwise a(m) = a(m−1) + m. The first few numbers in the Recaman’s Sequence is 0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9 · · · .

Given k, your task is to calculate a(k).

Input

The input consists of several test cases. Each line of the input contains an integer k where 0 ≤ k ≤ 500000. The last line contains an integer −1, which should not be processed.

Sample Input
7
10000
-1

Output

For each k given in the input, print one line containing a(k) to the output.

Sample output
20
18658