int led1 = 2;
int led2 = 3;
int led3 = 4;

void setup() {
 pinMode(led1, OUTPUT);
 pinMode(led2, OUTPUT);
 pinMode(led3, OUTPUT);
 }

void loop() {  
 digitalWrite(led1, HIGH)
 delay(1000);
 digitalWrite(led2, HIGH);
 delay(1000);
 digitalWrite(led3, HIGH);
 delay(1000); 


 digitalWrite(led1, LOW);
 delay(1000);
 digitalWrite(led2, LOW);
 delay(1000);
 digitalWrite(led3, LOW);
 delay(1000); 
 }