foo.cc: In function 'int main()':
foo.cc:14:21: warning: suggest parentheses around '+' inside '<<' [-Wparentheses]
   14 |         int O=1<<r-l+1;--O;
      |                  ~~~^~
foo.cc:21:23: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
   21 |             int x=1<<r-j,c1=ch[i][j],c2=ch[i][j-1],c3=ch[i-1][j];
      |                      ~^~

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