ac := sqrt(sqr(xa-xc) + sqr(ya-yc) + sqr(za-zc));
  bc := sqrt(sqr(xb-xc) + sqr(yb-yc) + sqr(zb-zc));
  ab := sqrt(sqr(xa-xb) + sqr(ya-yb) + sqr(za-zb));

//without this i have error
  if (ac = 0) or (bc = 0) or (ab = 0) then
    begin
    writeln(0);
    halt;
    end;
//end