function [a1,a3]=area(x0,xk1,a,r)
yk1=punish(x0,xk1,r);
h=0.0001;
a1=0;
a=a1;
y1=subs(yk1);
a2=h;
a=a2;
y2=subs(yk1);
if(y2>y1)
    h=-h;
    a3=a1;
    y3=y1;
    a1=a2;
    y1=y2;
    a2=a3;
    y2=y3;
end
a3=a2+h;
a=a3;
y3=subs(yk1);
while(y3<y2)
    h=2*h;
    a1=a2;
    y1=y2;
    a2=a3;
    y2=y3;
    a3=a2+h;
    a=a3;
    y3=subs(yk1);
end