import java.io.*;
import java.util.*;
import java.util.stream.*;

class Process {
    private int[] x;

    Process(int[] x) {
        this.x = x;
    }
    
    // 重複した要素がないか
    private boolean isUnique(int[] x) {
        return (x.length == IntStream.of(x).distinct().toArray().length);
    }
    
    // 等間隔か
    private boolean isEqualIntervals(int[] x) {
        int[] sortedX = IntStream.of(x).sorted().toArray();
        
        int interval = sortedX[1] - sortedX[0];
        for(int i = 1; i < (x.length - 1); i++) {
            if((sortedX[i + 1] - sortedX[i]) != interval) {
                return false;
            }
        }

        return true;
    }

    String getResult() {
        return ((isUnique(x) && isEqualIntervals(x)) ? "YES" : "NO");
    }
}

public class Main {
    public static void main(String[] args) throws IOException {
        var bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        var printWriter    = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));

        // 入力
        int N = Integer.parseInt(bufferedReader.readLine().trim());
        
        int[] x = Stream.of(bufferedReader.readLine().trim().split("[ ]+")).mapToInt(Integer::parseInt).toArray();

        // 処理および出力
        printWriter.println((new Process(x)).getResult());
        
        bufferedReader.close();
        printWriter.close();
    }
}