练习专区

The Recaman's sequence is defined by a(0)=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).

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.

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

7
10000
-1

20
18658