function F=importance(u)
%u=unifrnd(0,1,1,n);
%cg(u)=c*max(0,u-0.47)
IM=0.47+0.53*sqrt(u);
IMdens=2*(IM-0.47)./0.53^2;
FN=callopt(IM);
F=FN./IMdens;
IMest=mean(F)
IMvar=var(F)%IMest =
%    0.4615
%IMvar =
%  0.012817


