#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <string>
#include <cstdio>
#include <cmath>

using namespace std;

int N, X[100000005];

int main() {

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

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