已知平面向量 $\stackrel{\rightharpoonup }{a}$、 $\stackrel{\rightharpoonup }{b}$、 $\stackrel{\rightharpoonup }{c}$满足 $\stackrel{\rightharpoonup }{a}\perp \stackrel{\rightharpoonup }{b}$，且 $\left\{\left|\stackrel{\rightharpoonup }{a}\right|,\left|\stackrel{\rightharpoonup }{b}\right|,\left|\stackrel{\rightharpoonup }{c}\right|\right\}=\left\{1,2,3,\right\}$，则 $\left|\stackrel{\rightharpoonup }{a}+\stackrel{\rightharpoonup }{b}+\stackrel{\rightharpoonup }{c}\right|$的最大值是.