answer.code: In function ‘int main()’:
answer.code:30:17: error: return-statement with no value, in function returning ‘int’ [-fpermissive]
   30 |                 return ;
      |                 ^~~~~~
answer.code:48:21: error: return-statement with no value, in function returning ‘int’ [-fpermissive]
   48 |                     return ;
      |                     ^~~~~~
answer.code:51:29: error: ‘struct std::pair<std::_Rb_tree_const_iterator<int>, bool>’ has no member named ‘sy’
   51 |             sy.insert(y[u]).sy.insert(y[v]);
      |                             ^~