We report the first measurement of the absolute branching fraction of the inclusive decay Formula omitted. The analysis is performed using an Formula omitted collision data sample corresponding to an integrated luminosity of 567 Formula omitted taken at Formula omitted = 4.6 GeV with the BESIII detector. Using eleven Cabibbo-favored Formula omitted decay modes and the double-tag technique, this absolute branching fraction is measured to be Formula omitted, where the first uncertainty is statistical and the second systematic. The relative deviation between the branching fractions for the inclusive decay and the observed exclusive decays is Formula omitted, which indicates that there may be some unobserved decay modes with a neutron or excited baryons in the final state.