#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define ll long long
#define INF (1 << 30)
#define INFLL (1LL << 60)

int main() {
	int poppo[100010] = {};
	int n;
	cin >> n;
	for(int i = 0;i < n;i++){
		cin >> poppo[i];
	}
	sort(poppo, poppo + n);
	bool flag = false;
	int firstDiff = poppo[1] - poppo[0];
	for(int i = 1;i < n;i++){
		int nowDiff = poppo[i] - poppo[i - 1];
		if(nowDiff != firstDiff || poppo[i] == poppo[i-1]) flag = true;
	}
	if(flag) cout << "NO" << endl;
	else cout << "YES" << endl;
	return 0;
}