input: Write a function to calculate the maximum possible revenue from the items with given weights and values using the knapsack algorithm. The function should take in a list of weights, a list of values, and the number of items, and return the maximum revenue for a given capacity of the knapsack.
  assert knapsack([2, 1, 3], [4, 2, 3], 3)==5
  assert knapsack([1, 2, 3], [6, 10, 12], 3)==22
  assert knapsack([1, 1, 1], [10, 20, 30], 3)==50
  assert knapsack([2, 2, 2], [5, 5, 5], 3)==15
  assert knapsack([], [], 0)==0
output: def knapsack(weights, values, n):
      capacity = sum(weights)
      dp = [0] * (capacity + 1)
      
      for i in range(n):
          for w in range(capacity, weights[i] - 1, -1):
              dp[w] = max(dp[w], dp[w - weights[i]] + values[i])
      
      return max(dp)