unit Unit2;

interface
Function BS(N:integer; A:real):real;

implementation
Function BS(N:integer; A:real):real;
label 5,6,15;
var
    B:array[1..20] of real;
    DEL,R,EPS,S,AK,A2,DA,AJP,AJM,Q1,Q2,OMEG:real;
    M:integer;
begin
    If A = 0 Then
    begin
       If N / 2 = N / 2 Then
       begin
           B[N]:=0;
           GoTo 15;
       end;
       B[N]:=2 / N;
       GoTo 15;
    end;
    If Abs(A) < 8 Then
    begin
       DEL:=0.1e-7;
       If N / 2 <> N / 2 Then
       begin
           R:=2 / N;
           EPS:=R * DEL;
           S:=R;
           AK:=0;
           A2:=A * A;
5:         AK:=AK + 2;
           R:=R * A2 * (N + AK - 2) / (AK * (AK - 1) * (N + AK));
           S:=S + R;
           If R > EPS Then GoTo 5;
           B[N]:=S + R;
           GoTo 15;
       end;
       R:=2 * A / (N + 1);
       OMEG:=Abs(R * DEL);
       S:=R;
       AK:=1;
       A2:=A * A;
6:     AK:=AK + 2;
       R:=R * A2 * (N + AK - 2) / (AK * (AK - 1) * (N + AK));
       S:=S + R;
       If Abs(R) > OMEG Then GoTo 6;
       B[N]:=-(S + R);
       GoTo 15;
    end;
    DA:=1 / A;
    AJP:=DA * Exp(A);
    AJM:=(DA * DA) / AJP;
    B[1]:=AJP - AJM;
    If N = 1 Then GoTo 15;
    Q1:=-1;
    Q2:=1;
    For M:= 2 To N do
    begin
        B[M]:=Q1 * AJP - AJM + Q2 * DA * B[M - 1];
        Q1:=-Q1;
        Q2:=Q2 + 1;
    end;
15: BS:=B[N];
end;

end.