Observe the following $f$-block elements

$\mathrm{Eu}(Z=63) ; \mathrm{Pu}(Z=94) ; \mathrm{Cf}(Z=98)$;

$\operatorname{Sm}(Z=62) ; \mathrm{Gd}(Z=64) ; \mathrm{Cm}(Z=96)$

How many of the above have half-filled $f$-orbitals in their ground state?