//Exercise 1-3

int led1 = D2;
int led2 = D3;

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

void loop() {
    
    for(int i = 0; i <= 4; i++){
        if (i <= 4){
            digitalWrite(led1, HIGH);
            digitalWrite(led2, LOW);
            delay(500);
            
            digitalWrite(led1, LOW);
            digitalWrite(led2, HIGH);
            delay(500);
            
        }
    }
}