static void Main(string[] args)
{
Converter converter = new Converter(28, 30);
Console.WriteLine(converter.EURtoUAH(30));
Console.WriteLine(converter.UAHtoEUR(1000));
Console.WriteLine(converter.UAHtoUSD(2800));
Console.WriteLine(converter.USDtoUAH(500));
// bad tests! (throw exception for negative values) !!!!
Converter badConverter = new Converter(-28, -30);
Console.WriteLine(converter.USDtoUAH(-123));
}