#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define Would
#define you
#define please

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	int N;
	cin >> N;
	int X[100000];
	rep(i, N) cin >> X[i];
	sort(X, X + N);

	int D = X[1] - X[0];

	int OK = 1;
	if (D == 0) OK = 0;
	rep(i, N - 1) {
		if (D != X[i + 1] - X[i]) OK = 0;
	}

	if (OK) co("YES");
	else co("NO");



	Would you please return 0;
}