input: Write a function to calculate the total cost of groceries.
  assert total_cost({'apple': 3.99, 'banana': 2.99, 'milk': 5.99, 'bread': 3.50})==16.47
  assert total_cost({'apple': 1.20, 'banana': 0.80, 'milk': 1.50, 'bread': 1.00})==4.50
  assert total_cost({'apple': 2.99, 'banana': 1.99})==4.98
output: def total_cost(groceries):
      return sum(groceries.values())