int startPin = 8;
int numLeds = 4;
int x, y = startPin + numLeds -1;
int time_delay;

void setup() {
// put your setup code here, to run once
for(x = startPin; x < startPin + numLeds - 1; x++){
    pinMode(x, OUTPUT);
    pinMode(A0, INPUT);
}
}

void loop() {
// put your main code here, to run repeatedly:

time_delay = analogRead(A0);

for(x = startPin; x < startPin + numLeds - 1; x++){
digitalWrite(x, HIGH);
delay(time_delay);
digitalWrite(x, LOW);
delay(time_delay);
}

for(x = y; x > startPin; x--){
digitalWrite(x, HIGH);
delay(time_delay);
digitalWrite(x, LOW);
delay(time_delay);
}
}