#include <bits/stdc++.h>

using namespace std;

#define REP(i, n) for(int i = 0; i < n; i++)
#define FOR(i, m, n) for(int i = m; i < n; i++)
#define VSORT(v) sort(v.begin(), v.end())

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n;
    cin >> n;
    vector<int> a(n);
    REP(i, n) cin >> a[i];

    VSORT(a);
    int diff = a[1] - a[0];
    if (diff == 0) {
        cout << "NO" << endl;
        return 0;
    }

    FOR(i, 2, n) {
        if (a[i] - a[i - 1] != diff) {
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "YES" << endl;
    return 0;
}