const int led1=8;
const int led2=9;
const int led3=10;
const int led4=11;
void setup() {
  // put your setup code here, to run once:
  pinMode(led1, OUTPUT); 
  pinMode(led2, OUTPUT); 
  pinMode(led3, OUTPUT); 
  pinMode(led4, OUTPUT);
}
void loop() {
  // put your main code here, to run repeatedly: 
  digitalWrite(led1, LOW); 
  digitalWrite(led2, LOW); 
  digitalWrite(led3, LOW); 
  digitalWrite(led4, LOW); 
  delay(1000); 
  digitalWrite(led1, HIGH); 
  delay(1000); 
  digitalWrite(led2, HIGH); 
  delay(1000); 
  digitalWrite(led3, HIGH); 
  delay(1000); 
  digitalWrite(led4, HIGH);
  delay(1000);
}