input: Develop a python function to determine the position of the least significant set bit.
  assert get_rightmost_Set_Bit_Pos(12) == 3
  assert get_rightmost_Set_Bit_Pos(18) == 2
  assert get_rightmost_Set_Bit_Pos(16) == 5
output:     
      pos = 1
      while n > 0:
          if n & 1:
              return pos
          pos += 1
          n >>= 1
      return -1
  