Given an n x n grid of consecutive numbers, return the grid's Diamond Sum. The diamond sum is defined as the sum of the numbers making up the diagonals between adjacent sides.

Examples

diamondSum(1) ➞ 1

[1]

diamondSum(3) ➞ 20

[
  [1, _, 3],
  [_, 5, _],
  [7, _, 9]
]

// The numbers behind the underscores make up the Diamond Sum.
// 2 + 4 + 6 + 8 = 20

diamondSum(5) ➞ 104

[
  [1, 2, _, 4, 5],
  [6, _, 8, _, 10],
  [_, 12, 13, 14, _],
  [16, _, 18, _, 20],
  [21, 22, _, 24, 25]
]

// 3 + 7 + 9 + 11 + 15 + 17 + 19 + 23 = 104

Notes

• n is always an odd number.
• Bonus points for solving it mathematically!