foo.cc: In function 'void build(int, int, int)':
foo.cc:62:14: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   62 |     int mid=l+r>>1;
      |             ~^~
foo.cc: In function 'node ask(int)':
foo.cc:87:22: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   87 |     int mid=tree[x].l+tree[x].r>>1;
      |             ~~~~~~~~~^~~~~~~~~~
foo.cc: In function 'void lian(int)':
foo.cc:99:22: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   99 |     int mid=tree[x].l+tree[x].r>>1;
      |             ~~~~~~~~~^~~~~~~~~~

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