input: Write a python function to find the k-th smallest element in an array.
  assert kthSmallest([3,2,4,1,5], 3) == 3
  assert kthSmallest([10,20,15,25,5], 2) == 10
  assert kthSmallest([7,10,4,3,20,15], 4) == 10
output: def kthSmallest(arr, k):
      arr.sort()
      return arr[k-1]