input: Write a function to calculate the maximum possible revenue from the items with given weights and values. The function should take three parameters: a list of weights, a list of values, and the number of items. It should return the maximum revenue that can be obtained with a knapsack of capacity 5.
  assert knapsack([2, 1, 3], [4, 2, 3], 3)==7
  assert knapsack([1, 3, 4], [1, 1, 1], 3)==3
  assert knapsack([10, 20, 30], [60, 100, 120], 3)==220
  assert knapsack([1, 2, 3], [6, 10, 12], 3)==22
  assert knapsack([], [], 0)==0
output: def knapsack(weights, values, n):
      capacity = 5
      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 dp[capacity]