#include <iostream>
#include <algorithm>
using namespace std;
 
int main(){
	int N;
	cin >> N;
	int birds[N];
	for(int i = 0; i < N; i++){
		cin >> birds[i];
	}
	sort(birds, birds + N);
	int difference = birds[1] - birds[0];
	if(!difference){
		cout << "NO" << endl;
		return 0;
	}
	for(int i = 0; i < N - 2; i++){
		if(birds[i + 2] - birds[i + 1] != difference){
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
}