how to make a sequence in click in button click event

Question

i have a web form ,there are three buttons, like button 1 ,button 2 ,button 3,
i want that user cant make a jump from button 1 to button 3,he must follow the sequence. like

after entering date into the textbox user must follow these steps
 protected void Button1_Click(object sender, EventArgs e)
 { code }
 then 
  protected void Button2_Click(object sender, EventArgs e)
 { code }  
protected void Button1_Click(object sender, EventArgs e)
 { code }