using System;

using org.matheval;

public class Program

{

    public static void Main()

    {

        Expression expr = new Expression("IF(VALUE(LEFT(date,4))<2020,'n/a','generation of ' & LEFT(date,4))");

        expr.Bind("date", "2022-01-20");

        String value = expr.Eval<String>();     

        Console.WriteLine(value);

    }

}