input: Write a python function to solve the 0-1 knapsack problem using dynamic programming.
  assert knapsack(50, [10, 20, 30], [60, 100, 120], 3) == 220
  assert knapsack(100, [10, 20, 30, 40], [20, 30, 66, 40], 4) == 96
  assert knapsack(7, [1, 3, 4, 5], [1, 4, 5, 7], 4) == 9
output: def knapsack(W, wt, val, n):
      dp = [[0 for x in range(W + 1)] for x in range(n + 1)]
      
      for i in range(n + 1):
          for w in range(W + 1):
              if i == 0 or w == 0:
                  dp[i][w] = 0
              elif wt[i-1] <= w:
                  dp[i][w] = max(val[i-1] + dp[i-1][w-wt[i-1]], dp[i-1][w])
              else:
                  dp[i][w] = dp[i-1][w]
                  
      return dp[n][W]