function [x2] = szelop(f,a,b,N)
x0 = a;
x1 = b;
for k=1:N,
    x2 = x1-(polyval(f,x1)*(x1-x0))/(polyval(f,x1)-polyval(f,x0));
    x0 = x1;
    x1 = x2;
end;
