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

import static java.lang.System.in;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        int N = Integer.parseInt(reader.readLine());
        String[] inputs = reader.readLine().split(" ");
        int[] positions = Stream.of(inputs).mapToInt(Integer::parseInt).toArray();

        Arrays.sort(positions);
        int max = Integer.MIN_VALUE;
        int min = Integer.MAX_VALUE;
        for (int i = 1; i < N; i++) {
            int differences = positions[i] - positions[i - 1];
            max = Math.max(max, differences);
            min = Math.min(min, differences);
        }

        if (max == min && min != 0) {
            System.out.println("YES");
        } else {
            System.out.println("NO");
        }
    }
}