#include <stdio.h>
/* (a-1)^n + (a+1)^n mod a^2
* = n*a*(-1)^(n-1) + (-1)^n + n*a + 1
* = na*[(-1)^(n-1)+1] + (-1)^n + 1
* = if (n is odd) 2na else 2
*/
int rmax(int a)
{
int n = a / 2;
if (a % 2 == 0)
n--;
return 2 * n * a;
}
int main()
{
int sum = 0;
for (int a = 3; a <= 1000; a++)
sum += rmax(a);
printf("%d\n", sum);
}