  We measure the mass of the top quark in lepton$+$jets final states using the
full sample of $p\bar{p}$ collision data collected by the D0 experiment in Run
II of the Fermilab Tevatron Collider at $\sqrt s=1.96 $TeV, corresponding to
$9.7 {\rm fb}^{-1}$ of integrated luminosity. We use a matrix element technique
that calculates the probabilities for each event to result from $t\bar t$
production or background. The overall jet energy scale is constrained in situ
by the mass of the $W$ boson. We measure $m_t=174.98\pm0.76$ GeV. This
constitutes the most precise single measurement of the top-quark mass.
