int interruptpin = 2;
int ledpin=13;
volatile int p=1100;
int i=5;
void setup() {
  Serial.begin(9600);
  digitalWrite(2, HIGH);
  pinMode(ledpin, OUTPUT);
  pinMode(interruptpin,INPUT);
  digitalWrite(interruptpin, HIGH);
  attachInterrupt(0,gofast,LOW);
}

void loop() {
  Serial.println("hello");
  digitalWrite(ledpin, HIGH);
  delay(p);
  digitalWrite(ledpin, LOW);
  delay(p);
  digitalWrite(2, LOW);
}
void gofast(){
  p=100;
  Serial.println("Interrupt ");
}