using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var regexPattern = @"(?:^0?[1-5](?:\.[0-9])?\+?)(?:\s?\-\s?[1-6])?\s?\-?\s?months?\s?(?:contract(?:ed)?)?\s?(?:plus)?|^0?6(?:\.0)?\s?\-?\s?months?\s(?!plus|\+)|^0?6(?:\.0)?\s?\-?\s?months?$";

        var testStrings = new string[] {

            "6 months plus contract",

            "6 months",

            "4 month",

            "6 months"

        };

        var regex = new Regex(regexPattern, RegexOptions.CultureInvariant | RegexOptions.IgnoreCase | RegexOptions.ExplicitCapture | RegexOptions.Compiled);

        Console.WriteLine($"Does regexPattern match...\n");

        foreach (var s in testStrings) {

            var isRegexMatch = regex.IsMatch(s);

            Console.WriteLine($"'{s}' {string.Join("", System.Linq.Enumerable.Repeat('.', Math.Max(50, s.Length)-s.Length))} {isRegexMatch.ToString().ToUpper()}");

        }

    }

}