void setup() {
  pinMode(3, INPUT_PULLUP);
  pinMode(4,OUTPUT);
  digitalWrite(4, LOW);
  Serial.begin(9600);
  Serial.println("Aperte o botão!");
}

void loop() {
  digitalWrite(4, LOW);
  while(digitalRead(3)==0){
    digitalWrite(4, HIGH);
    delay(500);
    digitalWrite(4, LOW);
    delay(300);
  }
  
  
}