Abstract:  During the past decades, plenty of heavy hadrons have been observed in experiments, including quite a few exotic candidates. But the doubly and triply heavy flavor baryons are still absent in the hadron spectroscopy. There is a longstanding puzzle after the SELEX collaboration reporting an evidence of $\Xi_{cc}^+(ccd)$ in the final state of $\Lambda_c^+K^-\pi^+$ in 2002.   With much more data at LHCb, people failed to find it. After a careful study, we recommend the experimenters to search for $\Xi_{cc}^{++}(ccu)$ in the final states of $\Lambda_c^+K^-\pi^+\pi^+$ as the first priority. Finally, LHCb did reports the discovery of $\Xi_{cc}^{++}$ in the final state of $\Lambda_c^+K^-\pi^+\pi^+$ following our suggestion.