#include "bits/stdc++.h"

using namespace std;
using ll = long long;
const double pi = acos(-1);
#define FOR(i,a,b) for (ll i=(a),__last_##i=(b);i<__last_##i;i++)
#define RFOR(i,a,b) for (ll i=(b)-1,__last_##i=(a);i>=__last_##i;i--)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define __GET_MACRO3(_1, _2, _3, NAME, ...) NAME
#define rep(...) __GET_MACRO3(__VA_ARGS__, FOR, REP)(__VA_ARGS__)
#define rrep(...) __GET_MACRO3(__VA_ARGS__, RFOR, RREP)(__VA_ARGS__)
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v) {
	REP(i, v.size()) { if (i)os << " "; os << v[i]; }return os;
}
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v) {
	REP(i, v.size()) { if (i)os << endl; os << v[i]; }return os;
}

int main() {
	ll n;

	cin >> n;

	vector<ll> v(n);

	REP(i, n) {
		cin >> v[i];
	}

	sort(v.begin(), v.end());

	bool flag = true;

	if (v[1] - v[0] > 0) {
		ll x = v[1] - v[0];

		REP(i, n - 1) {
			if (v[i + 1] - v[i] != x) {
				flag = false;
				break;
			}
		}
	}
	else {
		flag = false;
	}

	if (flag) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}

}