int led1= 2;
int led2= 4;
int led3= 16;
int led4= 17;
void setup() {
 pinMode(2,OUTPUT);
 pinMode(4,OUTPUT);
 pinMode(16,OUTPUT);
 pinMode(17,OUTPUT);
}

void loop() {
 digitalWrite(led1,1);
 digitalWrite(led2,1);
 digitalWrite(led3,1);
 digitalWrite(led4,1);
 delay(500);
 digitalWrite(led1,0);
 digitalWrite(led2,0);
 digitalWrite(led3,0);
 digitalWrite(led4,0);
 delay(500);

}