static class Task4_4
{
    public static int BinSearch(IEnumerable<int> collection, int target, int left, int right)
    {
        if (left > right)
            return left; // позиция для вставки

        var mid = (left + right) / 2;
        var value = collection.ElementAt(mid);
        if (value == target)
            return mid;
        if (value < target)
            return BinSearch(collection, target, mid + 1, right);
        return BinSearch(collection, target, left, mid - 1);
    }
}