private static long[] GetTwoLastFibonacciSequenceElements(int n)
        {
            if (n <= 3)
            {
                return new long[] {1, 1};
            }
            else
            {
                var last = GetTwoLastFibonacciSequenceElements(n - 1);
                return new long[] {last[1], last[0] + last[1]};
            }
        }

        public static long GetFibonacciSequenceElement(int n)
        {
            var last = GetTwoLastFibonacciSequenceElements(n);
            return last[0] + last[1];
        }