"""
Number spiral diagonals
Problem 28
Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5 spiral is formed as follows:

                            21 22 23 24 25
                            20  7  8  9 10
                            19  6  1  2 11
                            18  5  4  3 12
                            17 16 15 14 13

It can be verified that the sum of the numbers on the diagonals is 101.

What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral formed in the same way?
"""

n = 3
diagonal_sum = 1
while n <= 1001:
    top_right_corner = n ** 2
    for i in range(0, 4):
        diagonal_sum += top_right_corner - (n-1) * i
    n += 2
print(diagonal_sum)