the problem, we also assume that all superconducting films are identical and can be described by a single critical temperature $T_{C}$ and coherence length $\xi _{S}.$ Transport properties of both sF and FS interfaces are also assumed identical and are characterized by the interface parameters $$\gamma =\frac{\rho _{S}\xi _{S}}{\rho _{F}\xi _{F}},\quad \gamma _{B}=\frac{R_{BF}\mathcal{A}_{B}}{\rho _{F}\xi _{F}}.  \label{gammas}$$Here $R_{BF}$ and $\mathcal{A}_{B}$ are the resistance and area of the sF and FS interfaces $\xi _{S}$ and $\xi _{F}$ are the decay lengths of S and F materials while $\rho _{S}$ and $\rho _{F}$ are their resistivities.

Under the above conditions the problem of calculation of the critical current in the SIsFS structure reduces to solution of the set of the Usadel equations[@Usadel]. For the S layers these equations have the form [@RevG; @RevB; @RevV] $$\frac{\xi _{S}^{2}}{\Omega G_{m}}\frac{d}{dx}\left( G_{m}^{2}\frac{d}{dx}\Phi _{m}\right) -\Phi _{m}=-\Delta _{m},~G_{m}=\frac{\Omega }{\sqrt{\Omega
^{2}+\Phi _{m}\Phi _{m}^{\ast }}},  \label{fiS}$$$$\Delta _{m}\ln \frac{T}{T_{C}}+\frac{T}{T_{C}}\sum_{\omega =-\infty
}^{\infty }\left( \frac{\Delta _{m}}{\left\vert \Omega \right\vert }-\frac{\Phi _{m}G_{m}}{\Omega }\right) =0,  \label{delta}$$where $m=S$ for $x\leq -d_{s}~$and$~x\geq d_{F};$ $m=s$ in the interval $-d_{s}\leq x\leq 0.$ In the F film $(0\leq x\leq d_{F})$ they are $$\xi _{F}^{2}\frac{d}{dx}\left( G_{F}^{2}\frac{d}{dx}\Phi _{F}\right) -\widetilde{\Omega }\Phi _{F}G_{F}=0.  \label{FiF}$$Here $\Omega =T(2n+1)/T_{C}$ are Matsubara frequencies normalized to $\pi
T_{C}$, $\widetilde{\Omega }=\Omega +iH/\pi 