private static void Test()
{
System.Diagnostics.Debug.WriteLine(F(1) * 2);
double F(int i) { return i > 1000 ? 0 : 1 + i / (2.0 * i + 1) * F(i + 1); }
}
{
System.Diagnostics.Debug.WriteLine(F(1) * 2);
double F(int i) { return i > 1000 ? 0 : 1 + i / (2.0 * i + 1) * F(i + 1); }
}