using System;

public class Program

{

    public static void Main()

    {

        //Fiscal Year start Oct 2019 To Sep 2020

        // using date 01-10-2019 should return FIscal Year 2020

        var date = new DateTime(2019, 10, 1);

        var startMonthOfFinancialYear = 10;

        Console.WriteLine("date: " + date);

        Console.WriteLine("GetFiscalFirstDate Year: " + GetFiscalFirstDate(date, startMonthOfFinancialYear).Year);

        Console.WriteLine("Get GetFinancialYear: " + GetFinancialYear(date, startMonthOfFinancialYear));

    }

     public static int GetFinancialYear( DateTime dateTime, int startMonthOfFinancialYear)

        {

            return (dateTime.Month >= startMonthOfFinancialYear) ? dateTime.AddYears(1).Year : dateTime.Year;

        }

    public static DateTime GetFiscalFirstDate(DateTime date,int fiscialMonth){

        var firstDay = new DateTime(date.Year,fiscialMonth,1);

        if(DateTime.Compare(firstDay, date) >= 0){

            firstDay = firstDay.AddYears(-1);

        }

        return firstDay;

    }

}