<image>Here is the translation of the specified math problem:

As shown in figure $$1$$, the two-ring triangle can be obtained as $$S=∠A_{1}+∠A_{2}+…+∠A_{6}=360^{\circ}$$. In the following figure $$2$$, the two-ring quadrilateral can be obtained as $$S=∠A_{1}+∠A_{2}+…+∠A_{7}=720^{\circ}$$. In figure $$3$$, the two-ring pentagon can be obtained as $$S=1080^{\circ}$$, $$…$$.

Clever students, based on the above pattern, please directly write out the result for the two-ring $$n$$-gon $$(n\geqslant 3 \text{ integer})$$, where $$S=$$ ______ degrees $$(use an algebraic expression containing $$n$$ to express the final result)$$.
