If $$\overrightarrow{a}, \overrightarrow{b}$$ and $$\overrightarrow{c}$$ are unit vectors satisfying $$\mid \overrightarrow{a} - \overrightarrow{b} \mid^2 + \mid \overrightarrow{b} - \overrightarrow{c} \mid^2 + \mid \overrightarrow{c} - \overrightarrow{a} \mid^2 = 9$$, then $$\mid 2 \overrightarrow{a} + 5 \overrightarrow{b} + 5 \overrightarrow{c}\mid$$ is