#define led4 19
#define led3 21
#define led2 22
#define led1 23

void setup() {
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
pinMode(led3, OUTPUT);
pinMode(led4, OUTPUT);
}

void loop(){

digitalWrite(led1, HIGH);
delay(1000);
digitalWrite(led1, LOW);
digitalWrite(led2, HIGH);
delay(1000);
digitalWrite(led2, LOW);
digitalWrite(led3, HIGH);
delay(1000);
digitalWrite(led3, LOW);
digitalWrite(led4, HIGH);
delay(1000);
digitalWrite(led4, LOW);
digitalWrite(led3, HIGH);
delay(1000);
digitalWrite(led3, LOW);
digitalWrite(led2, HIGH);
delay(1000);
digitalWrite(led2, LOW);
digitalWrite(led1, HIGH);
delay(1000);
digitalWrite(led1, LOW);
}