int x;

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

void loop(){ 
  if (Serial.available() > 0){
    x = Serial.read();
    switch(x){
      case 49:
        digitalWrite(3,0);
        break;
      case 50:
        digitalWrite(3,1);
        break;
      case 51:
        digitalWrite(4,0);
        break;
      case 52:
        digitalWrite(4,1);
        break;
    }
  }
}