import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;

public class No00000406_Main2 {
	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	public static void main(String[] args) throws IOException {
		int n = Integer.parseInt(br.readLine());
		String[] strArr = br.readLine().split(" ");
		int[] arr = new int[n];
		for(int i = 0; i < n; i++) arr[i] = Integer.parseInt(strArr[i]);
		Arrays.sort(arr);
		int dist = arr[1] - arr[0];
		for(int i = 0; i < n - 1; i++) {
			if(arr[i] == arr[i + 1] || dist != arr[i + 1] - arr[i]) {
				System.out.println("NO");
				return;
			}
		}
		System.out.println("YES");
	}
}