const int l1=13;
int td=1000;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(l1, OUTPUT);
}
void loop() {
  // put your main code here, to run repeatedly:
  if(td<=0){
    td=1000;
  }
  else if (td<550){
    td=td-250;
  }
  else {
    td=td-100;
  }
  digitalWrite(l1, HIGH);
  Serial.println(td);
  delay(td);
  digitalWrite(l1, LOW);
  Serial.println(td);
  delay(td);
  }