real a=3;
real b=3;
border C0(t=0,2*pi) {x=a*cos(t); y=b*sin(t); label=1;};
border C1(t=0,-2*pi) {x=a/2*cos(t); y=b/2*sin(t); label=2;};

int n=10;
mesh Th = buildmesh(C0(10*n)+C1(10*n));
plot(Th);