using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var x1 = "2021.09.02";

        var x2 = "2022.09.02";

        var a = ((DateTime.Parse(x2).Year - DateTime.Parse(x1).Year) * 12) + ((DateTime.Parse(x2).Month - DateTime.Parse(x1).Month) + 1);

        Console.WriteLine(a);

    }

}

​

​