Deleting numbers

Sereja has an array of n integers a[1], a[2], ..., a[n]. In one move Sereja can do the following operation Assume integers v and t, Where 1 ≤ v, t ≤ n, such that, all the elements of the array a[v], a[v + t], a[v + t * 2], ... a[v + t * k] Where k ≥ 0 are equal. To delete all elements a[v], a[v + t], a[v + t * 2], ... a[v + t * k] from the array. The remaining elements are written in a without