#define _USE_MATH_DEFINES	//M_PI(π),M_SQRT2(√2)
#include <iostream>			//std::cout, std::cin
#include <string>			//std::string,std::to_string(C++11)
#include <vector>			//std::vector
#include <valarray>			//std::valarray
#include <algorithm>		//std::sort
#include <time.h>			//localtime_s
#include <cstdlib>			//abs
#include <cmath>			//abs,std::pow,sqrt,sin,cos,round,floor,ceil
#include <fstream>			//std::ifstream,std::ofstream
#include <iomanip>			//std::setprecision,std::setw,std::setfill
#include <random>			//std::random(C++11)
#include <numeric>			//std::accumulate
#include <functional>		//std::greater

int main(void) {

	//test用
	//std::ifstream in("123.txt");
	//std::cin.rdbuf(in.rdbuf());

	int N = 0;
	std::cin >> N;
	std::vector<int> x(N);
	for (int i = 0; i < N; i++) {
		std::cin >> x[i];
	}
	std::sort(x.begin(), x.end());

	int basis = x[1] - x[0];
	bool flg = true;
	for (int i = 0; i < N - 1; i++) {
		int temp = x[i + 1] - x[i];
		if (basis != temp || temp == 0) {
			flg = false;
			break;
		}
	}

	if (flg) {
		std::cout << "YES" << std::endl;
	}
	else {
		std::cout << "NO" << std::endl;
	}

}