void setup()
{
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
   
}

void loop()
{
  int n,i;
  for(n=1;n<=25;n++)
  {
    digitalWrite(2,1);
    digitalWrite(3,1);
    digitalWrite(4,1);
    delay(1);

    for(i=1;i<=19;i++)
    {
      digitalWrite(2,0);
        if(i>6)
      digitalWrite(3,0);
        if(i>17)
      digitalWrite(4,0);
      delay(1);
    }
  }
  delay(500);
  
}