#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
using namespace std;
typedef long long LL;
typedef vector<int> VI;

int main() {
	int n;
	cin >> n;
	VI x;
	REP(i, n) {
		int t;
		cin >> t;
		x.push_back(t);
	}
	sort(ALL(x));
	int s = x[1] - x[0];
	string ans = (s == 0) ? "NO" : "YES";
	REP(i, n - 1) {
		if (x[i + 1] - x[i] != s) {
			ans = "NO";
		}
	}
	cout << ans << endl;
	return 0;
}