#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;
    for(int i=0; i<n-2; ++i) {
        ok &= (v[i+2]-v[i+1]) == (v[i+1]-v[i]);
    }
    if(ok) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}