#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;

int main(){
    long long n, t1, t2 = -1, d = 0;
    cin >> n;
    set<long long> st;
    for (int i = 0; i < n; i++){
        cin >> t1;
        if (!st.count(t1)) st.insert(t1);
        else {
            cout << "NO" << endl;
            return 0;
        }
    }
    d = *(++st.begin()) - *st.begin();
    for (auto x : st){
        t1 = x;
        if (t2 == -1){
            t2 = t1;
            continue;
        } else if (d != t1 - t2){
            cout << "NO" << endl;
            return 0;
        } else t2 = t1;
    }
    cout << "YES" << endl;
}