#include <iostream>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <map>
#include <queue>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using namespace std;

template<class T>
constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int n;
    cin >> n;
    vector<int> v(n);
    for (auto &&i : v) scanf("%d", &i);
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    if(v.size() != n){
        cout << "NO\n";
        return 0;
    }
    for (int i = 0; i < n - 2; ++i) {
        if(v[i+1]-v[i] != v[i+2]-v[i+1]){
            cout << "NO\n";
            return 0;
        }
    }
    cout << "YES\n";
    return 0;
}