int ledR = 13;
int ledG = 12;
int button = 7;
int blink;

void setup() {
  // put your setup code here, to run once:
  pinMode(ledG, OUTPUT);
  pinMode(ledR, OUTPUT);
  pinMode(button, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  blink = (digitalRead(button) == HIGH) ? ledG : ledR;
  digitalWrite(blink, HIGH);
  delay(500);
  digitalWrite(blink, LOW);
  delay(500);
}