add minutes to countdown

Hi,

I have a little program an countdown, and i want to have a button(button3) to add one minute to the time while the countdown is active.

thanks

namespace timer
{
public partial class Form1 : Form
{
private int TotalSeconds;
public Form1()
{
InitializeComponent();
}
private void timer1_Tick(object sender, EventArgs e)
{
if (TotalSeconds > 0)
{
TotalSeconds--;
int minutes = TotalSeconds / 60;
int seconds = TotalSeconds - (minutes * 60);
this.label1.Text = minutes.ToString() + ":" + seconds.ToString();
}
else
{
this.timer1.Stop();
MessageBox.Show("fim");
}
}
private void Form1_Load(object sender, EventArgs e)
{
for (int i = 0; i < 61; i++)
{
this.comboBox1.Items.Add(i.ToString("D2"));
this.comboBox2.Items.Add(i.ToString("D2"));
}
string minutos = ConfigurationManager.AppSettings["minutos"];
string segundos = ConfigurationManager.AppSettings["segundos"];
//label3.Text = minutos;
this.comboBox1.SelectedIndex = Int32.Parse(minutos);
this.comboBox2.SelectedIndex = Int32.Parse(segundos);
}
private void button1_Click_1(object sender, EventArgs e)
{
timer1.Start();
}
private void button2_Click(object sender, EventArgs e)
{
timer1.Stop();
}
private void button3_Click(object sender, EventArgs e)
{
timer1.Start();
}
public void button1_Click(object sender, EventArgs e)
{
int minutes = int.Parse(this.comboBox1.SelectedItem.ToString());
int seconds = int.Parse(this.comboBox2.SelectedItem.ToString());
TotalSeconds = (minutes * 60) + seconds;
this.timer1.Enabled = true;
}
private void button2_Click_1(object sender, EventArgs e)
{
this.timer1.Stop();
}
private void label4_Click(object sender, EventArgs e)
{
}
private void button3_Click_1(object sender, EventArgs e)
{
//**codigo que nao funciona
//TotalSeconds += 60;
}
}
}