#include<iostream>
#include<iomanip>
#include<cmath>
#include<string>
#include<algorithm>
#include<vector>
#include<math.h>
#include<stack>
using namespace std;
int main(void){
    long long N; cin >> N;
    int cnt = 1;
    long long x;
    vector<long long> v;
    for(int i = 0; i < N; i++){
        cin >> x;
        v.push_back(x);
    }
    sort(v.begin(), v.end());
    for(int i = 1; i < N -1; i++){
            if(v[i+1] - v[i] == v[i] - v[i-1] && v[i] != v[i-1]){
                continue;
            }else{
                cnt = 0;
                cout << "NO" << endl;
                break;
            }
    }
    if(cnt != 0) cout << "YES" << endl;
    return 0;
}