/// 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?
fn main() {
	let mut sum = 1;
	let mut add = 1;
	let mut inc = 5;
	let dinc = 8;
	let n = 1001;
	let steps = (n-1)/2;
	for _ in 0..steps {
		add += inc;
		sum += 4*add;
		inc += dinc;
	}
	println!("Answer: {}", sum);
}
