const int four=2;
unsigned long t0;
int N,Y;

void setup() {
  Serial.begin(9600);
  pinMode(four,OUTPUT);
}

void loop() {
  t0=millis();  
  N = analogRead(A0);     
  Serial.println(N);
  while (millis()-t0<500) {  // attente de 500 ms
       if (Serial.available()){
         Y=Serial.parseInt(); // Lecture de Y
         if (Y)digitalWrite(four,HIGH);
               else digitalWrite(four,LOW);
         while (Serial.available()) Serial.read();
       }  }
}