#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
using namespace std;
int main(void) {
	int n;
	cin >> n;
	vector<int> duck(n);
	for (int i = 0; i < n; ++i) cin >> duck[i];
	sort(duck.begin(), duck.end());
	set<int> st;
	int diff;
	for (int i = 0; i < n - 1; ++i) {
		diff = duck[i + 1] - duck[i];
		st.insert(diff);
	}
	if (st.size() == 1 && diff != 0) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
	return 0;
}