#define motorPin 10

void setup() {
  pinMode(motorPin, OUTPUT);
  Serial.begin(9600);
  while (! Serial);
  Serial.println("Speed 0 to 255");
  Serial.println("But use 50 to 255 because minimum V required to start the motor is 50");
}

void loop() {
  {
    if (Serial.available())
    {
      int speed = Serial.parseInt();
      if (speed >= 50 && speed <= 255)
      {
        analogWrite(motorPin, speed);
      }
    }
  }

}