#define _USE_MATH_DEFINES

#include <iostream>		//cin, cout
#include <vector>		//vector
#include <algorithm>	//sort,min,max,count
#include <string>		//string,getline, to_string
#include <cstdlib>		//abs(int)
#include <utility>		//swap, pair
#include <deque>		//deque
#include <climits>		//INT_MAX
#include <bitset>		//bitset
#include <cmath>		//sqrt, ceil. M_PI, pow, sin
#include <ios>			//fixed
#include <iomanip>		//setprecision
#include <sstream>		//stringstream
#include <numeric>		//gcd, assumlate
#include <random>		//randam_device
#include <limits>		//numeric_limits

using namespace std;
constexpr long long int D_MOD = 1000000007;

int main() {

	int N;
	cin >> N;

	vector<int> x(N);
	for (int i = 0; i < N; i++) {
		cin >> x[i];
	}

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

	for (int i = 1; i < N - 1; i++) {
		if (x[i] == x[i - 1]) {
			cout << "NO" << endl;
			return 0;
		}
		if (x[i] - x[i - 1] != x[i + 1] - x[i]) {
			cout << "NO" << endl;
			return 0;
		}
	}

	cout << "YES" << endl;

	return 0;

}