const int led1 = 0;

void setup() 
{
  pinMode(led1, OUTPUT);
}
int delayTime = 1000;

void loop() 
{
  while (delayTime > 0){
    digitalWrite(led1, HIGH);
    delay(delayTime);
    digitalWrite(led1, LOW);
    delay(delayTime);
    delayTime = delayTime - 100;
  }
  while (delayTime < 1000){
    delayTime = delayTime + 100;
    digitalWrite(led1, HIGH);
    delay(delayTime);
    digitalWrite(led1, LOW);
    delay(delayTime); 
  }
}