input: Write a python function to calculate the total number of visitors from a list.
  assert calculate_total_visitors([2000, 1500, 2500, 1800]) == 7800
  assert calculate_total_visitors([100, 200, 300]) == 600
  assert calculate_total_visitors([0, 0, 0, 0]) == 0
output: def calculate_total_visitors(visitors_list):
      return sum(visitors_list)