How to manually specify DF in PROC GLIMMIX

proc glimmix data=sample METHOD=LAPLACE ;
*where flag_CE=1 ;
where flag_SAT=1 ;
*where flag_DE=1 ;
class group_school ;
model enroll_fall=treat pretest_GPA male minority disadv /
solution /*ddfm=kr*/ dist=binomial link=logit
ddf=36.157,.,.,.;
random intercept /subject=group_school;
run;