Double Integral in polar coordinates

Hi. I have a problem with the answer of this integral code:

 syms r theta 
 a = r*cos(theta);
 b = r*sin(theta);
 Q = (1/(2*pi*L)) * exp( - (a^2 + b^2)/(2*L))*f;
 q = int(int(Q,r,0,L),theta,0,pi/2);

Where the values of L and f are calculated in the code before this integral. But the answer of q is 1*1sym and it doesn't show the value. I really appreciate if you let me know my mistake.

Thanks