import java.util.Arrays;

public class Test {

  public static void main(String[] args) {
    Integer[] a = {8, 7, 6, 4, 3, 2, 1, 0};
    Arrays.sort(a);
    int n = a.length - 1;
    for (int i = 0; i < n; i++) {
      if (!(a[i] == i)) {
        System.out.println(i); // 5
        break;
      }
    }

  }
}