作者mayuka

Z=X+(X-Y)/(Y-1)+1───＞
Z＝X+(X-Y)/(Y-1)＋(Y-1)/ (Y-1)＝X+(X-1)/(Y-1)＝(XY-X)/(Y-1)＋(X-1)/(Y-1)＝(XY-1)/(Y-1)
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