int led=7;
int led2=4;
int led3=2;

void setup() 
{
 // put your setup code here, to run once;
  pinMode(led, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
}

void loop() 
{
  // put your setup code here, to run once;
digitalWrite(led, HIGH);
delay(500);
digitalWrite(led,LOW);
delay(500);
digitalWrite(led2, HIGH);
delay(500);
digitalWrite(led2, LOW);
delay(500);
digitalWrite(led3, HIGH);
delay(500);
digitalWrite(led3,LOW);
delay(500);
digitalWrite(led, HIGH);
delay(500);
digitalWrite(led,LOW);
delay(500);
digitalWrite(led2, HIGH);
delay(500);
digitalWrite(led2, LOW);
delay(500);
digitalWrite(led3, HIGH);
delay(500);
digitalWrite(led3,LOW);
delay(500);
digitalWrite(led, HIGH);
digitalWrite(led2, HIGH);
digitalWrite(led3, HIGH);
delay(500);
digitalWrite(led,LOW);
digitalWrite(led2, LOW);
digitalWrite(led3, LOW);
delay(500);
digitalWrite(led, HIGH);
digitalWrite(led3, HIGH);
delay(500);
digitalWrite(led,LOW);
digitalWrite(led3, LOW);
delay(500);
}