#include<iostream>
#include<algorithm>
using namespace std;
int main() {
	int n; cin >> n;
	long long a[114514]; for (int i = 0; i < n; i++)cin >> a[i]; sort(a, a + n);
	for (int i = 1; i < n - 1; i++)if (a[i] - a[i - 1] != a[i + 1] - a[i] || a[i - 1] == a[i] || a[i] == a[i + 1]) {
		cout << "NO\n"; return 0;
	}
	cout << "YES\n";
}