const int firstLed = 3; 
const int secondLed = 5;
const int thirdLed = 6;
int brightness = 0;
int increment = 1;
void setup()
{
 pinMode(3, OUTPUT);
pinMode(5,OUTPUT);
pinMode(6, OUTPUT);
}
void loop()
{
 if(brightness > 255)
 {
 increment = -1; 
 }
 else if(brightness < 1)
 {
 increment = 1; 
 }
 brightness = brightness + increment; 
 
 analogWrite(firstLed, brightness);
 analogWrite(secondLed, brightness);
 analogWrite(thirdLed, brightness );
 delay(10); 
}