#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <deque>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <ctime>
#include <iterator>
#include <bitset>
#include <numeric>
#include <list>
#include <iomanip>
#include <cassert>
#include <array>
#include <tuple>
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <forward_list>
using namespace std;
using ll = long long;
#define rep(i,k) for (int i = 0; i < (int)(k); i++)
#define all(cnt) begin(cnt), end(cnt)

int main() {
    int n;
    while (cin >> n) {
        vector<int> a(n);
        for (int i = 0; i < n; i++) {
            cin >> a[i];
        }
        sort(a.begin(), a.end());
        bool ok = true;
        for (int i = 1; i < n - 1; i++) {
            int d1 = a[i] - a[i - 1];
            int d2 = a[i + 1] - a[i];
            if (d1 != d2 || d1 == 0) ok = false;
        }
        cout << (ok ? "YES" : "NO") << endl;
    }
}