int number = 0; // for incoming serial data

void setup() {
  Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
}

void loop() {
  // send data only when you receive data:
    if (Serial.available() > 0) {
    // read the incoming byte:
    number = Serial.parseInt();
    digitalWrite(number, !digitalRead(number));
    // say what you got:


    }
  }