using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        int i = 20140820;

        Console.WriteLine($"StringParse:{StringParse.Parse(i)}");

        Console.WriteLine($"MathParse:{MathParse.Parse(i)}");

    }

}

​

public static class StringParse

{

    public static DateTime Parse(int i)

    {

        return DateTime.ParseExact(

            i.ToString().AsSpan(),

            "yyyyMMdd".AsSpan(),

            CultureInfo.InvariantCulture);

    }

}

​

public static class MathParse

{

    public static DateTime Parse(int i)

    {

        return new DateTime(

                Math.DivRem(Math.DivRem(i, 100, out var day), 100, out var month),

                month,

                day);

    }

}