Let $\overrightarrow{u},\overrightarrow{v},\overrightarrow{w} $ be such that $|\overrightarrow{u}|=1,|\overrightarrow{v}|=2,|\overrightarrow{w} |=3 $. If the projection $\overrightarrow{v} $ along $\overrightarrow{u} $ is equal to that of $\overrightarrow{w} $ along $\overrightarrow{u} $ and $\overrightarrow{v} $ and $\overrightarrow{w} $ are $\bot$ to each other , then $|\overrightarrow{u} -\overrightarrow{v} +\overrightarrow{w} |$ equals