/in/foo.cc: In function 'void tarjan(long long int, long long int)':
/in/foo.cc:27:25: warning: unused variable 'w' [-Wunused-variable]
      auto v = i.first , w = i.second ;
                         ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:123:14: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
         mid=l+r>>1;
             ~^~