procedure MIDPNT(A, B:real;var S:real; N:integer);
var
    TNM,DEL,DDEL,X,SUM:real;
    J,IT:integer;
begin
    If N = 1 Then
    begin
        S:=(B - A) * FUNC(0.5 * (A + B));
        IT:=1;
    end
    Else
    begin
        IT:=Trunc(Exp((N - 2)*Ln(3)));
        TNM:=IT;
        DEL:=(B - A) / (3 * TNM);
        DDEL:=DEL + DEL;
        X:=A + 0.5 * DEL;
        Sum:=0;
        For J:=1 To IT do
        begin
            Sum:=Sum + FUNC(X);
            X:=X + DDEL;
            Sum:=Sum + FUNC(X);
            X:=X + DEL;
        end;
        S:=(S + (B - A) * Sum / TNM) / 3;
    end;
end;