The positive odd numbers are sorted in ascending order as 1,3,5,7,9,11,13,15,17,19…………….,and grouped as (1), (3,5), (7,9,11), (13,15,17,19) and so on. Thus, the first group is(1) , the second group is (3,5), the third group is (7,9,11), etc. In general, the kth group contains the next k elements of the sequence. Given k, find the sum of the elements of the kth group.

Constraints  1 ≤ k ≤ 106

Subtasks  For 50% of the maximum score, k<103