input: Write a python function to find the minimum number in a list.
  assert find_min_num([12, 24, 9]) == 9
  assert find_min_num([10, 5, 8, 3, 2]) == 2
  assert find_min_num([7, 7, 7, 7, 7]) == 7
output: def find_min_num(lst):
      return min(lst)