#include<bits/stdc++.h>
#define rep(i, x) for(ll i = 0; i < x; i++)
#define rep2(i, x) for(ll i = 1; i <= x; i++)
#define all(a) (a).begin(),(a).end()
using ll = long long;
using ld = long double;
const ll INF = 10000000000000000;
using namespace std;
signed main() {
	ll n, cnt = 0; cin >> n; vector<ll> v(n);
	rep(i, n) { cin >> v[i]; }
	sort(all(v));
	rep(i, n) {
		if (i == 0) { continue; }
		else if (i == 1) { cnt = v[i] - v[i - 1]; }
		else if (v[i] - v[i - 1] != cnt) { cout << "NO\n"; }
	}
	cout << "YES\n";
	return 0;
}