A hemispherical vessel is completely filled with a liquid of refractive index μ.A small coin is kept at the lowest point (O) of the vessel as shown

A hemispherical vessel is completely filled with a liquid of refractive index μ. A small coin is kept at the lowest point (O) of the vessel as shown in figure. The minimum value of the refractive index of the liquid so that a person can see the coin from point E (at the level of the vessel)  is _____                       

                                                                 (JEE-2025)