program Project1075_chala;

{$APPTYPE CONSOLE}

uses
  SysUtils, math;

  const
  EPS = 0.0000001;

    var
    xa, xb, xc, ya, yb, yc, za, zb, zc, r : integer;
    AB, BC, AC, cos_gamma, cos_gamma1, yoy, vatar, d, h : real;

begin
   read(xa, ya, za);
   read(xb, yb, zb);
   read(xc, yc, zc);
   read(r);
   AB := sqrt(sqr(xb-xa)+sqr(yb-ya)+sqr(zb-za));
   AC := sqrt(sqr(xc-xa)+sqr(yc-ya)+sqr(zc-za));
   BC := sqrt(sqr(xb-xc)+sqr(yb-yc)+sqr(zb-zc));
   if AB + BC <= AC+EPS then d := AB-2*r+PI*r
   else
     if (AC+EPS >= BC + AB) or (BC+EPS >= AC + AB) then d := AB
     else
       begin
         cos_gamma := (AC*AC+BC*BC-AB*AB)/(2*AC*BC);
         h := AC*BC*sqrt(1 - sqr(cos_gamma))/AB;
       if h+EPS >= r then d := AB
       else
         begin
           vatar := 2 * sqrt(sqr(r)-sqr(h));
           cos_gamma1 := (2*sqr(r)-sqr(vatar))/(2*r*r);
           yoy := arccos(cos_gamma1) * r;
           d := AB - vatar + yoy;
         end;
       end;
   writeLn(d:0:2);
end.

thanks

  const
  EPS = 0.000001;

    var
    xa, xb, xc, ya, yb, yc, za, zb, zc, r : integer;
    c, a, b, yoy, vatar, d, h : real;

begin
   read(xa, ya, za);
   read(xb, yb, zb);
   read(xc, yc, zc);
   read(r);
   c := sqr(xa-xb)+sqr(ya-yb)+sqr(za-zb);     //AB^2
   d := sqrt(c);
   b := sqr(xa-xc)+sqr(ya-yb)+sqr(za-zc);     //AC^2
   a := sqr(xb-xc)+sqr(yb-yc)+sqr(zb-zc);     //BC^2
   h := (4*a*b-sqr(a+b-c))/(4*c);
   if sqrt(h) < r then
     if sqrt(b-h)+sqrt(a-h)-EPS<=d then
       begin
         vatar := 2*sqrt(sqr(r)-h);
         yoy := r*arccos((2*h-sqr(r))/(r*r));
         d := d - vatar + yoy;
       end;
   writeLn(d:0:2);
end.

Solution is wrong, because you must search for kasatelnye(russian word)

kasatelnye == tangent