/in/foo.cc: In function 'int erfen(int)':
/in/foo.cc:21:12: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   int mid=l+r>>1;
           ~^~
/in/foo.cc:26:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:40:7: warning: unused variable 'l' [-Wunused-variable]
   int l=1,r=top;
       ^
/in/foo.cc:40:11: warning: unused variable 'r' [-Wunused-variable]
   int l=1,r=top;
           ^