int counter = 0;

void setup() {
  // put your setup code here, to run once:
  pinMode(5, OUTPUT); //red light
  pinMode(6, OUTPUT); //green light
}

void loop() {
  // put your main code here, to run repeatedly:
  int result = 0;
  int red_timer = 500;
  int green_timer = 700;

  result = counter / red_timer;
  if (result % 2 == 0) {
    digitalWrite(5, HIGH);
  } else {
    digitalWrite(5, LOW);
  }

  result = counter / green_timer;
  if (result % 2 == 0) {
    digitalWrite(6, HIGH);
  } else {
    digitalWrite(6, LOW);
  }
  
  delay(1);
  counter = counter + 1;
}