#define _CRT_SECURE_NO_DEPRECATE

#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<string>

#include<queue>

#include<vector>

#include<time.h>

#include<cmath>

#include<set>

using namespace std;

typedef long long int LL;

const int MAX =  + ;

int main(){

//#ifdef kirito

//    freopen("in.txt", "r", stdin);

//    freopen("out.txt", "w", stdout);

//#endif

    int n,num;

    while (~scanf("%d", &n)){

        set<int>se;

        for (int i = ; i < n; i++){

            scanf("%d", &num); se.insert(num);

        }

        if (se.size()>){

            printf("NO\n");

        }

        else if (se.size() == ){

            vector<int>m;

            for (set<int>::iterator it = se.begin(); it != se.end(); it++){

                m.push_back(*it);

            }

            sort(m.begin(), m.end());

            if (m[] - m[] == m[] - m[]){

                printf("YES\n");

            }

            else{

                printf("NO\n");

            }

        }

        else{

            printf("YES\n");

        }

    }

    return ;

}