foo.cc: In function 'void build(int, int, int)':
foo.cc:63:14: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   63 |     int mid=l+r>>1;
      |             ~^~
foo.cc: In function 'tree ask(int)':
foo.cc:88:19: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   88 |     int mid=t[x].l+t[x].r>>1;
      |             ~~~~~~^~~~~~~
foo.cc: In function 'void lian(int)':
foo.cc:100:19: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
  100 |     int mid=t[x].l+t[x].r>>1;
      |             ~~~~~~^~~~~~~

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