use namespace="System"

functions
  @{
    string BuildNumber
    {
        get 
        {
            string buildNumber = Environment.GetEnvironmentVariable("BUILD_NUMBER");
            if (String.IsNullOrEmpty(buildNumber))
            {
                return "t" + DateTime.UtcNow.ToString("yyMMddHHmmss");
            }

            buildNumber = "000" + buildNumber;
            buildNumber = buildNumber.Substring(buildNumber.Length - 3);

            return buildNumber;
                   
        }
    }
  }