You are going to act as a Python interpreter. You will be given a valid python program below. Write down what you think the result of its execution would be. Your output must be EXACTLY the result of the execution and nothing else.
situation
system
def knapsack(weights, values, capacity):
  # Create a matrix to store the maximum values at each nth item
  matrix = [[0 for x in range(capacity+1)] for x in range(len(weights)+1)]

  # Fill in the matrix
  for i in range(len(weights)+1):
    for j in range(capacity+1):
      # If the capacity is 0 or there are no items to choose, the value is 0
      if i == 0 or j == 0:
        matrix[i][j] = 0
      # If the current item is less than or equal to total capacity
      elif weights[i-1] <= j:
        # Choose between the maximum of not including the item versus including it
        matrix[i][j] = max(values[i-1] + matrix[i-1][j-weights[i-1]],  \
                           matrix[i-1][j])
      # If it is larger, the maximal value is without the item
      else:
        matrix[i][j] = matrix[i-1][j]

  # Return the top right corner of the matrix
  return matrix[len(weights)][capacity]

weights = [1,2,2,3,4]
values = [5,6,8,10,11]  
capacity = 5
print(knapsack(weights, values, capacity))
# Expected output: 18
user
19
assistant