int ledPin1 = 3;
int ledPin2 = 5;
int ledPin3 = 6;

void setup() {
  Serial.begin(9600);
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
  pinMode(ledPin3, OUTPUT);
}

void loop() {
  breathe(ledPin1);
  breathe(ledPin2);
  breathe(ledPin3);
}
void breathe(int ledPin) {
  int brightness = 0;
  int fadeAmount = 5;
  while (brightness < 255) {
    brightness += fadeAmount;
    analogWrite(ledPin, brightness);
    delay(30);
  }
  while (brightness > 0) {
    brightness -= fadeAmount;
    analogWrite(ledPin, brightness);
    delay(30); 
  }
}