#include<iostream>
#include<string>
#include<cstring>
#include<complex>
#include<vector>
#include<algorithm>
#include<cstdlib>
#include<cmath>
using namespace std;

#define REP(i, j) for (int i = 0; i < (int)j; ++i)
#define FOR(i, j, k) for (int i = (int)j; i < (int)k; ++i)
#define SORT(v) sort(v.begin(), v.end())
#define REVERSE(v) reverse(v.begin(), v.end())
typedef complex<double> P;
typedef vector<int> VI;
typedef long long LL;
typedef pair<int,int> PII;

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

	int n;
	cin >> n;
	VI duck;
	REP(i,n) {
		int x;
		cin >> x;
		duck.push_back(x);
	}
	SORT(duck);

	int diff = duck[1] - duck[0];
	bool flg = true;
	FOR(i,2,n) {
		if (diff == 0 || duck[i] - duck[i-1] != diff) {
			cout << "NO" << endl;
			flg = false;
			break;
		}
	}

	if (flg) cout << "YES" << endl;

	return 0;
}