static void Main(string [] args)
{
int [] a = { 3, 6, 1, 7, 2, 8, 4, 9, 10 };
var bit = new BIT(a.Length);
bit.Build(a);
bit.Print();
Console.WriteLine(bit.Sum(a.Length - 1));
bit.Update(3, 2);
Console.WriteLine(bit.Sum(1, 3));
}