function answer=graygrid(img);

answer=zeros(5,5);

for x=1:5
  for y=1:5
    for i=1:5
      for j=1:5
        answer(x,y)=answer(x,y)+img(5*(x-1)+i,5*(y-1)+j);
      end
    end
    answer(x,y)=answer(x,y)/25;
  end
end