input: def sum_squares(lst):
      """"
      This function processes a list of integers. It squares each integer if its index is divisible by 3, cubes each integer if its index is divisible by 4 but not by 3, and leaves other integers unchanged. Finally, it returns the sum of all the modified integers.
      
      Examples:
      For lst = [1,2,3] the output should be 6
      For lst = []  the output should be 0
      For lst = [-1,-5,2,-1,-5]  the output should be -126
      """
output:     result = 0
      for i, num in enumerate(lst):
          if i % 3 == 0:
              result += num ** 2
          elif i % 4 == 0:
              result += num ** 3
          else:
              result += num
      return result