foo.cc: In function 'int main()':
foo.cc:7:6: warning: unused variable 'xa' [-Wunused-variable]
  int xa=x1,xb=x2;
      ^~
foo.cc:7:12: warning: unused variable 'xb' [-Wunused-variable]
  int xa=x1,xb=x2;
            ^~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。