Random Led Blinker

int yellow=2;
int red=5;
int green=8;
int blue=12;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(yellow,OUTPUT);
  pinMode(red,OUTPUT);
  pinMode(green,OUTPUT);
  pinMode(blue,OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
    int a = random(1,5);

    switch(a){
      case 1:
        digitalWrite(yellow,HIGH);
        delay(1000);
        digitalWrite(yellow,LOW);
        break;

      case 2:
        digitalWrite(red,HIGH);
        delay(1000);
        digitalWrite(red,LOW);
        break;

      case 3:
        digitalWrite(green,HIGH);
        delay(1000);
        digitalWrite(green,LOW);
        break;

      case 4:
        digitalWrite(blue,HIGH);
        delay(1000);
        digitalWrite(blue,LOW);
        break;
    }
}