{\sqrt{{r_1^2 + \dots + r_{2 \cdot 2006}^2} \over {2 \cdot 2006}}} \ge 
{{r_1 + \dots + r_{2 \cdot 2006}} \over {2 \cdot 2006}} = {{2006} \over {2 \cdot 2006}} = {1 \over 2}