$\displaystyle \frac{2+998}{2} \cdot 499$\displaystyle \frac{2+998}{2} \cdot 499

$\displaystyle \frac{2+1000}{2} \cdot 500$\displaystyle \frac{2+1000}{2} \cdot 500

$\displaystyle \frac{2+1001}{2} \cdot 500$\displaystyle \frac{2+1001}{2} \cdot 500

$\displaystyle \frac{1+1001}{2} \cdot 1001$\displaystyle \frac{1+1001}{2} \cdot 1001