#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
using ll = long long;
using namespace std;
const int INF = 1e9;

int main() {
    int N;
    cin >> N;
    vector<int> A(N);
    rep(i, N) cin >> A[i];
    sort(A.begin(), A.end());

    bool flag = true;
    int sa = A[1] - A[0];
    if (sa == 0)
        flag = false;
    rep(i, N - 1) if (A[i + 1] - A[i] != sa)
        flag = false;

    flag ? cout << "YES" : cout << "NO";
    cout << endl;

    return 0;
}