void setup() {
  Serial.begin(115200);
  pinMode(2, OUTPUT);
  pinMode(4, INPUT);
}
void loop() {
  int v=digitalRead(4);
  if (v==1) {
    digitalWrite(2, HIGH);  
    Serial.println("Led is on");
      }else{
        digitalWrite(2,LOW);
        Serial.println("Led is off");
      }
      delay(1000);
}