Question: quadruple Integral

Good afternoon, to successfully complete my study on beam vibration i wrote a matlab code to produce all my calculations. This is the beginning of the ocde and shows the point were i get stuck:

prod2=5/2*  3200/4507*sin(pi*alp)*sin(pi*bet)/s*sin(pi*x)*pi^4*sin(pi*y)+19200/4507*sin(pi*alp)*sin(pi*bet)/s^5*sin(pi*x)*sin(pi*y)-6400/4507*sin(pi*alp)*sin(pi*bet)/s^3*sin(pi*x)*pi^2*sin(pi*y))*pi*exp(-5*(x^2-2*x*alp+alp^2-y^2+2*y*bet-bet^2)^(1/2))

 Im aware of its large extent but i must calculate the quadriple integral of this function, my thought was to write:

hj=int(int(int(int(prod2,x,0,a),y,0,b),alp,d1,d2),bet,k1,k2);

NOTE: the variable to integrate are x,y,alp(alpha) and bet(beta). That goes from 0,a ; 0,b ; d1,d2 ; k1,k2 

respectively. 

When typing its response it says

"Error using ==> sym.maple
Error, (in collect/series) too many levels of recursion"