#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int main() {
	int N; cin >> N;
	vector<int> x(N);
	for (int i = 0; i < N; i++)
		scanf("%d", &x[i]);
	sort(x.begin(), x.end());
	for (int i = 0; i + 2 < N; i++)
		if (x[i + 1] - x[i] != x[i + 2] - x[i + 1]) {
			cout << "NO" << endl;
			return 0;
		}
	if (x.front() == x.back()) {
		cout << "NO" << endl;
		return 0;
	}
	cout << "YES" << endl;
}