int led_red=4;
int led_yellow =5;
int led_blue=6;
void setup()
{ 
 pinMode(led_red, OUTPUT);
 pinMode(led_yellow, OUTPUT);
 pinMode(led_blue, OUTPUT);
 }
void loop()
{ 
digitalWrite(led_red, HIGH);
digitalWrite(led_yellow, LOW);
digitalWrite(led_blue, LOW);
delay (2000);
digitalWrite(led_red, LOW);
digitalWrite(led_yellow, LOW);
digitalWrite(led_blue, HIGH);
delay (3000);
digitalWrite(led_red, LOW);
digitalWrite(led_yellow, HIGH);
digitalWrite(led_blue, LOW);
delay (4000);
}