int r=0;
void interrupt_3() {
  r++;
  Serial.println(r);
}

void setup() {
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);
  attachInterrupt(digitalPinToInterrupt(3),interrupt_3,RISING);
}

void loop() {
  if (r>=5) {
    r=0;
    digitalWrite(LED_BUILTIN,!digitalRead(3));
  }
}