  Although nodeless superconducting gap has been observed on the large Fermi
pockets around the zone corner in KxFe2-ySe2, whether its pairing symmetry is
s-wave or nodeless d-wave is still under intense debate. Here we report an
isotropic superconducting gap distribution on the small electron Fermi pocket
around the Z point in KxFe2-ySe2, which favors the s-wave pairing symmetry.
