int n,m;
void setup() 
{
  pinMode(2,OUTPUT);
  n = 0;
  m = 0;

}

void loop() 
{
  if(n<25)
  {
    digitalWrite(2,1);
    delay(m);
    digitalWrite(2,0);
    delay(20-m);
  }
  else
  {
    delay(5);
    n=0;
    m = m+1;
    if(m>20)
    m = 0;
  }
  n =n+1;
 
}