System.Globalization.CultureInfo culture = System.Globalization.CultureInfo.CreateSpecificCulture("fr-FR");
DateTime date1 = DateTime.Parse(project.Variables["v1"].Value, "dd/MM/yyyy", culture);
DateTime date2 = DateTime.Parse(project.Variables["v2"].Value, "dd/MM/yyyy", culture);
int days = (date2 - date1).Days;
return days;