int led_red = 6; // the red LED is connected to Pin 6 of the Arduino
int led_blue = 5; // the blue LED is connected to Pin 5 of the Arduino
int led_green = 3; // the green LED is connected to Pin 3 of the Arduino

void setup() {
  // set up all the LEDs as OUTPUT
  pinMode(led_red, OUTPUT);
  pinMode(led_blue, OUTPUT);
  pinMode(led_green, OUTPUT);
}

void loop() {
  // turn the green LED on and the other LEDs off
  digitalWrite(led_red, LOW); 
  digitalWrite(led_blue, LOW);
  digitalWrite(led_green, HIGH);
  delay(1000);    // wait 1 seconds
  
  // turn the blue LED on and the other LEDs off
  digitalWrite(led_red, LOW);   
  digitalWrite(led_blue, HIGH);
  digitalWrite(led_green, LOW);
  delay(1000);   // wait 1 second
  
  // turn the red LED on and the other LEDs off
  digitalWrite(led_red, HIGH);  
  digitalWrite(led_blue, LOW);
  digitalWrite(led_green, LOW);
  delay(1000);  // wait 1 seconds        
}