foo.cc: In function 'void build(int, int, int)':
foo.cc:27:17: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   27 |     int mid = l + r >> 1;
      |               ~~^~~
foo.cc: In function 'int ask(int, int, int)':
foo.cc:36:23: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   36 |     int mid = tr[u].l + tr[u].r >> 1;
      |               ~~~~~~~~^~~~~~~~~

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