int num;   // my count down number is global

void setup()
{
  size(600, 600);
  colorMode(HSB);
  frameRate(1);
  num = 10;        // init the count down number
}

void draw()
{
  background(0);   // black background
  fill(255);       // color for text
  textAlign(CENTER, CENTER);
  if (num==0) {
    textSize(80);
    text("BLAST OFF!", width/2.0, height/2.0);
    stop();
  } 
  else {
    textSize(200);
    text(str(num), width/2.0, height/2.0);
  }
  num = num - 1;
}