  The Parisi formula for the free energy of the Sherrington-Kirkpatrick model
is completed to a closed-form generating functional. We first find an integral
representation for a solution of the Parisi differential equation and represent
the free energy as a functional of order parameters. Then we set stationarity
equations for local maxima of the free energy determining the order-parameter
function on interval $[0,1]$. Finally we show without resorting to the replica
trick that the solution of the stationarity equations leads to a marginally
stable thermodynamic state.
