type FunctionType = function(x: real): real;

function f(x: real): real; begin f := x end;

function IntegralSimpson(a, b: real; f: FunctionType; e: real): real;
  var
    h, x, s, s1, s2, s3, sign: real;
 begin

  if (a = b) then
    begin
      IntegralSimpson := 0; exit
    end;

  if (a > b) then
    begin
      x := a; a := b; b := x; sign := -1
    end
   else sign:=1;

  h := b - a; s := f(a) + f(b); s2 := s;

  repeat
    s3 := s2; h := h/2; s1 := 0; x := a + h;

    repeat
      s1 := s1 + 2*f(x); x := x + 2*h;
    until (not(x < b));

    s := s + s1; s2 := (s + s1)*h/3; x := abs(s3 - s2)/15
  until (not(x > e));

  IntegralSimpson := s2*sign;
 end;

begin

  writeln(IntegralSimpson(0, 1, f, 0.001));
  writeln; writeln('Press Enter'); readln;
end.