int pushButton = 12;
int GREEN = 8;
int YELLOW = 9;
int RED = 10;
// the setup routine runs once when you press reset:
void go();
void stop();
void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  // make the pushbutton's pin an input:
  pinMode(pushButton, INPUT);
  pinMode(GREEN, OUTPUT);
  pinMode(YELLOW, OUTPUT);
  pinMode(RED, OUTPUT);
}
void go(){
  digitalWrite(RED, LOW);
  digitalWrite(GREEN, HIGH);
};
void stop(){
  digitalWrite(GREEN, LOW);
  if(digitalRead(RED)==LOW){
    digitalWrite(YELLOW, HIGH);
    delay(500);
    digitalWrite(YELLOW, LOW);
  }
  digitalWrite(RED, HIGH);
};

// the loop routine runs over and over again forever:
void loop() {
  // read the input pin:
  int buttonState = digitalRead(pushButton);
  // print out the state of the button:
  Serial.println(buttonState);
  if(buttonState == 1) go();
  else stop();
  delay(1);  // delay in between reads for stability
}