{$n+}
program kaz;
  var
  l,x,x1,x2,y,y1,y2,st1,st2,st3,rast,ydl,per,h,opr:extended;
begin
    read(x1);
    read(y1);
    read(x2);
    readln(y2);
    read(x);
    read(y);
    read(l);
    st1:=sqrt(sqr(x1-x)+sqr(y1-y));
    st2:=sqrt(sqr(x2-x)+sqr(y2-y));
    st3:=sqrt(sqr(x2-x1)+sqr(y2-y1));
    per:=(st1+st2+st3)/2;
    h:=sqrt(per)*sqrt(per-st1)*sqrt(per-st2)*sqrt(per-st3)*2/st3;
    opr:=sqrt(st1*st1-h*h)+sqrt(st2*st2-h*h)-0.00001;
    if opr<st3 then ydl:=h-l
    else
    if st1<st2 then ydl:=st1-l
    else ydl:=st2-l;
    if st1>st2 then rast:=st1-l
    else rast:=st2-l;
    if rast<0 then  rast:=0;
    if ydl<0 then  ydl:=0;
    writeln(ydl:1:2);
    writeln(rast:1:2);
end.

st3 can be equal to zero.
I changed your code: if st3=0 then h:=st1 else ...
And I've got AC!

 I am very happy.