int ledGreen =13;  
int ledYellow =10;  
int ledRed =7;  

void setup() {
  pinMode(ledGreen, OUTPUT);
  pinMode(ledYellow, OUTPUT);
  pinMode(ledRed, OUTPUT);
}

void loop() {
  
digitalWrite(ledGreen, HIGH);
digitalWrite(ledRed, LOW);
digitalWrite(ledYellow, LOW);
delay(3000);

digitalWrite(ledGreen, LOW);
digitalWrite(ledRed, LOW);
digitalWrite(ledYellow, HIGH);
delay(1000);

digitalWrite(ledGreen, LOW);
digitalWrite(ledRed, HIGH);
digitalWrite(ledYellow, LOW);
delay(2000);
}