int led_pin_1 = 2;
int led_pin_2 = 4;

void setup() {
 pinMode(led_pin_1, OUTPUT);
pinMode(led_pin_2, OUTPUT);

}

void loop() {
 digitalWrite(led_pin_1 , HIGH);
 delay(1000);
 digitalWrite(led_pin_1 , LOW);
 delay(1000);
 digitalWrite(led_pin_2 , HIGH);
 delay(1000);
 digitalWrite(led_pin_2 , LOW);
 delay(1000);

}