using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var a = new int[] {123456, 5, 654321, 1234567890};

        foreach (var n in a) {

            Console.WriteLine($"Reversed = {Reverse(n)}");  

        }

    }

    private static int Reverse(int input) {

        var stack = BuildStack(input);

        return ConvertStackToNumber(stack);

    }

​

    private static Stack<int> BuildStack(int input) {

        var power = 0;

        var stack = new Stack<int>();

        while (true) {

            power++;

            var modBy = (int) Math.Pow(10, power);

            var divisior = (int) Math.Pow(10, power - 1);

            var remainder = (input % modBy) / divisior;

            if (remainder == 0 && power != 1) break;

            stack.Push(remainder);

        }

        return stack;

    }

    private static int ConvertStackToNumber(Stack<int> stack) {

        var total = 0;

        var power = 0;

        while (stack.Count > 0) {

            var current = stack.Pop();

            total += current * (int)Math.Pow(10, power++);

        }

        return total;

    }

}