#include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <bitset>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;
typedef long long ll;
typedef pair<int,int> pint;
typedef vector<int> vint;
typedef vector<pint> vpint;
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)

int main(void){
	int n; cin >> n;
	vector<int> x(n);
	rep(i, n) cin >> x[i];
	sort(all(x));
	int sa = x[1] - x[0];
	if(sa == 0){
		printf("NO\n");
		return 0;
	}
	for (int i = 1; i < n - 1; ++i){
		if(sa != x[i + 1] - x[i]){
			printf("NO\n");
			return 0;
		}
	}
	printf("YES\n");
	return 0;
}