input: Write a python function to calculate the summation of the largest and smallest numbers in a list.
  assert sum_of_min_max([1, 2, 3, 4, 5]) == 6
  assert sum_of_min_max([-10, -5, 0, 5, 10]) == 0
  assert sum_of_min_max([7, 7, 7, 7, 7]) == 14
  assert sum_of_min_max([1]) == 2
output: def sum_of_min_max(lst):
      return min(lst) + max(lst)