Function arcsinala(X : real):real;
Const E = 2.9e-19;
Var Temp : real;
    arcsin : real;
    N : Word;
Function Pow(A,B:real):real;
Var T:Real;
Begin
     T := Abs(A);
     Pow := Exp(B*Ln(T));
End;
Function ElemMakloren(A:integer):Real;
Var I : integer;
    Result : Real;
Begin
     If A > 1 Then Begin
        Result := 1;
        For I := 1 To A-1 Do Begin
            If I mod 2 = 0 Then Result := Result / I
                           Else Result := Result * I;
        End;
        If A mod 2 = 0 Then Result := 0;
        If A >= 3 Then Result := Result * Pow(X,A) / A;
     End Else Result := A * X;
     ElemMakloren := Result;
End;
Begin
     arcsin := 0;
     N := 1;
     Temp := 1;
     While Temp >= E Do Begin
           Temp := ElemMakloren(N);
           arcsin := arcsin + Temp;
           N := N + 2;
     End;
     arcsinala:=arcsin;
End;
{--------------------}
 
begin
    writeln(arcsinala(0.9):4:9);
end.