import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int[] x = new int[N];
    for(int i = 0; i < N; i++) {
      x[i] = sc.nextInt();
    }
    Arrays.sort(x);
    String ans = "YES";
    if(x[1] == x[0]) ans = "NO";
    for(int i = 2; i < N; i++) {
      if(x[i] - x[i - 1] != x[1] - x[0]) {
        ans = "NO";
        break;
      }
    }
    System.out.println(ans);
  }
}