int led1 = 5;
int led2 = 6;
int sw = 3;
volatile int currentLED = led1;
void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(sw, INPUT_PULLUP);
  attachInterrupt(1, LED, FALLING);
}
void loop() {
  for (int i = 0; i < 256; i++) {
    analogWrite(currentLED, i);
    delay(5);
  } for (int i = 255; i > 0; i--) {
    analogWrite(currentLED, i);
    delay(5);
  }
}
void LED() {
  if (currentLED == led1) {
    analogWrite(led1, 0);
    currentLED = led2;
  } else if (currentLED == led2) {
    analogWrite(led2, 0);
    currentLED = led1;
  }
  //detachInterrupt(1);
}