int RED = 8;
int GREEN = 7;
int YELLOW = 6;
int BLUE = 5;
void setup ()
{
  pinMode (RED, OUTPUT);
  pinMode (GREEN, OUTPUT);
  pinMode (YELLOW, OUTPUT);
  pinMode (BLUE, OUTPUT);
}
void loop ()
{
  digitalWrite (RED, HIGH);
  digitalWrite (GREEN, LOW);
  digitalWrite (YELLOW, LOW);
  digitalWrite (BLUE, LOW);
  delay (1000);
  digitalWrite (RED, LOW);
  digitalWrite (GREEN, HIGH);
  digitalWrite (YELLOW, LOW);
  digitalWrite (BLUE, LOW);
  delay (1000);
  digitalWrite (RED, LOW);
  digitalWrite (GREEN, LOW);
  digitalWrite (YELLOW, HIGH);
  digitalWrite (BLUE, LOW);
  delay (1000);
  digitalWrite (RED, LOW);
  digitalWrite (GREEN, LOW);
  digitalWrite (YELLOW, LOW);
  digitalWrite (BLUE, HIGH);
  delay (1000);
}