Left panel: fit of the inclusive \ee yield in the 10\% most central \PbPb collisions at \fivenn as a function of DCA$_{\rm ee}$ in the mass range $1.2 < m_{\rm ee} < 2.6$ \GeVmass. Right panel: corresponding $\chi^{2}$ as a function of the two fit parameters, i.e. the ratio of the yield of \ee pairs originating from a prompt source or from open-charm hadron decays to the measured \ee yield. See text for more details.