foo.cc:33:2: error: #endif without #if
   33 | #endif
      |  ^~~~~
foo.cc: In function 'int dfs(int, int, int)':
foo.cc:14:4: warning: control reaches end of non-void function [-Wreturn-type]
   14 | dfs(x+1,used+1,now^a[x]);
      | ~~~^~~~~~~~~~~~~~~~~~~~~

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