// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int main() {
    // Input
    int N;
    cin >> N;
    vector<int> x(N);
    rep(i, N) cin >> x[i];

    // Judge
    sort(x.begin(), x.end());
    string ans = "YES";
    int dist = x[1] - x[0];
    if (dist == 0) ans = "NO";
    rep(i, N-1) if (x[i+1] - x[i] != dist) ans = "NO";

    // Output
    cout << ans << endl;
}