How can I get curvature contour

I got my surface plot from

Schwarz = @(x,y,z) cos(x) + cos(y) + cos(z);
fimplicit3(Schwarz);

and now I would like to add my own contour line

which created base on curvature (k).

which k can be calculated by (the function of x, y, z)

syms x y z 
    
f = cos(x) + cos(y) + cos(z);

fx = diff(f,x);
fy = diff(f,y);
fz = diff(f,z);

fxx = diff(fx,x);
fxy = diff(fx,y);
fxz = diff(fx,z);

fyx = diff(fy,x);
fyy = diff(fy,y);
fyz = diff(fy,z);

fzx = diff(fz,x);
fzy = diff(fz,y);
fzz = diff(fz,z);

mat = [fxx fxy fxz fx; fyx fyy fyz fy; fzx fzy fzz fz; fx fy fz 0];
no = det(mat);
de = (fx^2 + fy^2 + fz^2)^2;
k = de/no;

how can I add my curvature contour line ?