// No.406 鴨等間隔の法則
// https://yukicoder.me/problems/no/406
//

#include <iostream>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>
#include <regex>
#include <utility>
#include <unordered_map>
#include <map>
#include <set>
#include <regex>
#include <iomanip>
#include <sstream>
#include <array>
using namespace std;

string solve(vector<int> ducks);


int main() {
    int N;
    cin >> N;

    vector<int> ducks;
    for (auto i = 0; i < N; i++) {
        int tmp;
        cin >> tmp;
        ducks.push_back(tmp);
    }

    string ans = solve(ducks);
    cout << ans << endl;
}

string solve(vector<int> ducks) {
    sort(ducks.begin(), ducks.end());
    int diff;
    diff = ducks[1] - ducks[0];
    if (diff == 0)
        return "NO";

    for (auto i = 2; i < ducks.size(); i++ ) {
        if (ducks[i] - ducks[i-1] != diff)
            return "NO";
    }
    return "YES";
}