private void button_ask_Click(object sender, EventArgs e)
        {
            string curr1 = textBox_curr1.Text;
            string curr2 = textBox_curr2.Text;

            if (curr1 == string.Empty || curr2 == string.Empty)
            {
                MessageBox.Show("Enter curr1 and curr2 pls!");
                return;
            }

            string answ = _client.AskServer(curr1, curr2);

            textBox_answer.Text += answ + "\r\n";
        }