Lemda_function_01

ll res = -1e12;
      function<ll(ll, ll)> dfs = [&](ll u, ll parent) -> ll {
        ll mx1 = 0, mx2 = 0;

        for (auto v : adj[u]) {
            if (v != parent) {
                ll tmp = dfs(v, u);

                if (tmp > mx1) {
                    mx2 = mx1;
                    mx1 = tmp;
                } else if (tmp > mx2) {
                    mx2 = tmp;
                }
            }
        }

        res = max(res, mx1 + mx2 + val[u]);
        return max(mx1, mx2) + val[u];
     };


      dfs(1, -1);