#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vl = vector<ll>;     using vvl = vector<vl>;

#define REP(i,n) for(ll i = 0; i < (n); ++i)
#define ALL(c) (c).begin(), (c).end()

int main() {
	cin.tie(0);
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(50);
	ll n; cin >> n;
	vl x(n); REP(i, n) cin >> x[i];
	sort(ALL(x));
	x.erase(unique(ALL(x)), x.end());
	if (x.size() != n) {
		cout << "NO" << endl;
		return 0;
	}

	ll diff = abs(x[1] - x[0]);
	REP(i, x.size() - 1) if (diff != x[i + 1] - x[i]) {
		cout << "NO" << endl;
		return 0;
	}
	cout << "YES" << endl;


	return 0;
}