int buttonstate;
void setup() {
  pinMode(13, OUTPUT);
  pinMode(4, INPUT);
}

void loop() {
  buttonstate=digitalRead(4);
  if(buttonstate==HIGH){
    digitalWrite(13, HIGH);
    delay(1000);
    digitalWrite(13, LOW);
    delay(1000);
  }
  else{
    digitalWrite(13, LOW);
  }
}