//#include <atcoder/all>
#include <bits/stdc++.h>
#include <cmath>
using namespace std;
//using namespace atcoder;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
Graph G;
vll E;
vector<bool> seen;

int main() {
	ll N;
	cin>>N;
	vll X(N);
	rep(i,N)cin>>X[i];
	sort(all(X));
	set<ll> S;

	rep(i,N-1){
		if(X[i]==X[i+1]){
			cout<<"NO"<<endl;
			return 0;
		}
		S.insert(X[i+1]-X[i]);
	}
	cout<<(S.size()==1?"YES":"NO")<<endl;
	
}