#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> v(n);
    for(int i=0; i<n; ++i) {
        cin >> v[i];
    }
    sort(v.begin(), v.end());
    bool ok = true;
    int d = v[1]-v[0];
    for(int i=0; i<n-1; ++i) {
        ok &= d == v[i+1]-v[i] && v[i] != v[i+1];
    }
    if(ok) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}