int LED = 12;
int btn = 4; 

void setup() { 
  // put your setup code here, to run once: 
 pinMode(LED, OUTPUT); 
 pinMode(btn, INPUT_PULLUP); 
 digitalWrite(LED, LOW); 
}

void loop()  { 
  // put your main code here, to run repeatedly:
   if(digitalRead(btn)== LOW){ 
    digitalWrite(12, HIGH); 
    delay(200); 
    digitalWrite(12, LOW); 
    delay(200); 
   } 
}