void setup() {
  // put your setup code here, to run once:
  pinMode(0, OUTPUT);
   pinMode(20, INPUT);
}


void loop() {
  // put your main code here, to run repeatedly:
  while(digitalRead(20)==HIGH){
    analogWrite(0,0);
   delay(1000);
    analogWrite(0,100);
   delay(1000);
   analogWrite(0,300);
    delay(1000);
   analogWrite(0,500);
    delay(1000);
}
analogWrite(0,0);
}