#define LED 2

int a;

void setup() {
  Serial.begin(115200);
  Serial.println("Hello, ESP32!");
  pinMode(LED,OUTPUT);
  Serial.print("Enter seconds for which LED glows: ");
  while(Serial.available()==0);
  a = Serial.parseInt();
  Serial.println(a);
}

void loop() {
  digitalWrite(LED,HIGH);
  delay(a*1000);
  digitalWrite(LED,LOW);
  delay(a*1000);
}