#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <cmath>
#include <iomanip>
#define rep(i, n) for(int i = 0; i < (int)(n); ++i)
#define PI acos(-1)
using namespace std;

int main() {
    int N;
    cin >> N;
    vector<int> X(N);
    rep(i, N) cin >> X[i];
    sort(X.begin(), X.end());
    bool judge = true;
    for (int i = 2; i < N; ++i) {
        if (X[i - 1] == X[i]) judge = false;
        if (X[i - 2] - X[i - 1] != X[i - 1] - X[i]) judge = false;
    }
    cout << (judge ? "YES\n" : "NO\n");
    return 0;
}