/in/foo.cc: In function 'int main()':
/in/foo.cc:44:18: warning: 'l' may be used uninitialized in this function [-Wmaybe-uninitialized]
     int u, v, w, l, r, mx = -1;
                  ^
/in/foo.cc:82:20: warning: 'r' may be used uninitialized in this function [-Wmaybe-uninitialized]
     x = l; while (x!=r) {dfs2 (x, 0); x = fa[x];} dfs2 (r, 0);
                   ~^~~