foo.cc: In function 'int main()':
foo.cc:15:19: warning: left operand of comma operator has no effect [-Wunused-value]
 for (int i=0,j=0;i<=2*n,j<=n;i+=2,j++)
                  ~^~~~~

自豪的采用jd5进行评测(github.com/masnn/jd5)

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