int f = 5;
int s = 6;
int x = 2000;
void setup() {
pinMode(f, OUTPUT);
pinMode(s, OUTPUT);
}
void loop() {
  while( x <= 2000 ){
    if(x == 0){
  x = 2000;}
digitalWrite(f, LOW);
delay(x);
digitalWrite(f, HIGH);
delay(x);
digitalWrite(s,LOW);
delay(x);
digitalWrite(s, HIGH);
 delay(x);
 x= x - 500 ;}
}