#include <bits/stdc++.h>
using namespace std;
int main() {
       	int n, flag = 0;
       	cin >> n;
       	vector<int> x(n);
       	for(int i = 0; i < n; i++) cin >> x[i];
       	sort(x.begin(), x.end());

       	int keep;
       	if(x[0] != x[1]) {
       		keep = x[1] - x[0];
       		for(int i = 2; i < n; i++) {
       			if(keep != x[i] - x[i - 1]) {
       				flag = 1;
       				break;
       			}
       		}
       	} else {
       		flag = 1;
       	}

       	if(flag) {
       		cout << "NO" << endl;
       	} else {
       		cout << "YES" << endl;
       	}

       	return 0;
}