Error 207: Invalid floating point operation

uses graph, crt; 
var  
Dr,Md,x,y,r,x2,y2,r2,xs1,ys1,xs2,ys2,rx,ry :integer; 
sx,sy: string;
rasst: real;
begin
  randomize;
  Dr:= Detect;
  InitGraph(Dr,Md,'');
  x:=Random(GetMaxX);
  y:=Random(GetMaxY);
  r:=Random(10)+5;
  x2:=Random(GetMaxX);
  y2:=Random(GetMaxY);
  r2:=Random(10)+5;
  repeat
    xs1:=Random(4)-2;
    ys1:=Random(4)-2;
    xs2:=Random(4)-2;
    ys2:=Random(4)-2;
  until ((xs1<>0) or (ys1<>0)) and ((xs2<>0) or (ys2<>0));
  repeat
    SetColor(2);
    Circle(x,y,r);
    SetColor(14);
    Circle(x2,y2,r2);
    x:=x+xs1;
    y:=y+ys1;
    x2:=x2+xs2;
    y2:=y2+ys2;
    if ((x-r<0) or (x+r>GetMaxX)) then xs1:=-xs1;
    if ((y-r<0) or (y+r>GetMaxY)) then ys1:=-ys1;
    if ((x2-r2<0) or (x2+r2>GetMaxX)) then xs2:=-xs2;
    if ((y2-r2<0) or (y2+r2>GetMaxY)) then ys2:=-ys2;
    rx:=abs(x2-x);
    ry:=abs(y2-y);
    rasst:=sqrt(sqr(rx)+sqr(ry));
    if rasst<(r+r2) then
    begin
      xs1:=-xs1;
      xs2:=-xs2;
      ys1:=-ys1;
      ys2:=-ys2;
    end;
    delay(10);
    cleardevice;
  until keypressed;
  CloseGraph;
end.