#include <iostream>
#include <fstream>
#include <vector>
#include <cstring>
#include <string>
#include <algorithm>
#include <iomanip>
using namespace std;
template<typename T> void setmin(T& a, T& b) { a = min(a, b); }
template<typename T> void setmax(T& a, T& b) { a = max(a, b); }

int x[100000];

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

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

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

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