/in/foo.cc: In function 'int main()':
/in/foo.cc:15:21: warning: suggest parentheses around '+' inside '<<' [-Wparentheses]
         int O=1<<r-l+1;--O;
                  ~~~^~
/in/foo.cc:22:23: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
             int x=1<<r-j,c1=ch[i][j],c2=ch[i][j-1],c3=ch[i-1][j];
                      ~^~