/in/foo.cc: In function 'int unionn(int, int)':
/in/foo.cc:15:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:22:8: warning: iteration 30000 invokes undefined behavior [-Waggressive-loop-optimizations]
   f[i] = i;
   ~~~~~^~~
/in/foo.cc:20:18: note: within this loop
  for(int i = 1;i <= maxn;i++)
                  ^