/in/foo.cc: In function 'int main()':
/in/foo.cc:48:5: warning: statement has no effect [-Wunused-value]
    q;
     ^
/in/foo.cc:22:12: warning: iteration 24 invokes undefined behavior [-Waggressive-loop-optimizations]
   gongxu[i]=1;
   ~~~~~~~~~^~
/in/foo.cc:21:15: note: within this loop
  for(int i=1;i<=MAXN;i++){
               ^