hello world, esp8266

main.ino

#include <ESP8266WiFi.h>

void setup() {
  Serial.begin(115200);

  Serial.println("Setup");
  pinMode(D2, OUTPUT);
}

void loop() {
  static int state = LOW;

  if (state == LOW) {
    digitalWrite(D2, HIGH);
    state = HIGH;
  } else {
    digitalWrite(D2, LOW);
    state = LOW;
  }

  delay(1000);
}

: error: 'D2' was not declared in this scope
digitalWrite(D2, HIGH);