input: def find_index(arr, x):
      """ Find the index of the value in the array or return -1 if not present
      >>> find_index([2, 5, 9, 15], 5)
      1
      >>> find_index([2, 5, 9, 15], 3)
      -1
      """
      for i in range(len(arr)):
          if arr[i] == x:
              return i
      return -1
output:     for i in range(len(arr)):
          if arr[i] == x:
              return i
      return -1