Motor controlled by serial

//Arduino PWM Speed Control：
int E1 = 5;
int M1 = 4;

void setup() {
    pinMode(M1, OUTPUT);
    Serial.begin(9600);
}

void loop() {
  if (Serial.available()) {
    int value = Serial.parseInt();
    if (value != 0) {
      if (value > 0) {
          digitalWrite(M1, HIGH);
      } else {
          digitalWrite(M1, LOW); // Go backwards
      }
      value = abs(value);

      if (value < 5) {
              analogWrite(E1, 0);
      } else {
        value = map(value, 0, 90, 50, 255);
        analogWrite(E1, value);
      }
      delay(2);
    }
  }
}