#include <iostream>
#include <vector>
#include <algorithm>

#define REP(i, a, b) for (int i = int(a); i < int(b); i++)

using namespace std;

typedef long long int lli;

int main() {
    int N;
    cin >> N;
    vector<int> v(N);
    REP (i, 0, N) cin >> v[i];
    sort(begin(v), end(v));
    int dis = v[1] - v[0];
    REP (i, 0, N - 1) {
        if (v[i + 1] - v[i] != dis) {
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << (dis ? "YES" : "NO") << endl;
    return 0;
}