input: Write a function to calculate the maximum possible revenue from items with given weights and values using the knapsack algorithm. The function should take in three parameters: a list of weights, a list of values, and the total number of items. The knapsack has a capacity of 5 units. If the number of items is zero, return 0.
  assert knapsack([2, 1, 3], [4, 2, 3], 3)==7
  assert knapsack([1, 2], [2, 4], 2)==6
  assert knapsack([3, 2, 1], [5, 3, 4], 3)==9
  assert knapsack([], [], 0)==0
  assert knapsack([1, 1, 1], [1, 1, 1], 3)==3
output: def knapsack(weights, values, n):
      if n == 0:
          return 0
      capacity = 5
      dp = [[0] * (capacity + 1) for _ in range(n + 1)]
      for i in range(1, n + 1):
          for w in range(1, capacity + 1):
              if weights[i-1] <= w:
                  dp[i][w] = max(dp[i-1][w], dp[i-1][w-weights[i-1]] + values[i-1])
              else:
                  dp[i][w] = dp[i-1][w]
      return dp[n][capacity]