#define _USE_MATH_DEFINES

#include <iostream>	//cin, cout
#include <vector>	//vector
#include <algorithm> //sort,min,max,count
#include <string>	//string,getline
#include <ios>		//fixed
#include <iomanip>	//setprecision
#include <utility> //swap
#include <cstdlib>	//abs(int)
#include <cmath>	//sqrt
#include <sstream>	//stringstream,getline
#include <cmath>	//ceil,M_PI

using namespace std;

int main() {

	int N;
	cin >> N;

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

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

	int sa = A[1] - A[0];
	if (sa == 0) {
		cout << "NO" << endl;
		return 0;
	}

	for (int i = 2; i < N; i++) {
		if (sa != A[i] - A[i - 1]) {
			cout << "NO" << endl;
			return 0;
		}
	}

	cout << "YES" << endl;
	return 0;

}