input: def transform_and_sum(lst):
      """
      This function processes a list of integers. It squares the integer values located at indices which are multiples of 3 and cubes the values located at indices which are multiples of 4 but not multiples of 3. For all other indices, it leaves the integers unchanged. It then returns the sum of the modified list.
      
      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:     total = 0
      for i, val in enumerate(lst):
          if i % 3 == 0:
              total += val ** 2
          elif i % 4 == 0:
              total += val ** 3
          else:
              total += val
      return total