#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <math.h>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> a(n,0);
    for(int i = 0;i < n;i++){
        cin >> a[i];
    }
    sort(a.begin(), a.end());
    string ans = "YES\n";
    for(int i = 2;i < n;i++){
        if(a[i-2] == a[i-1] || a[i-1] == a[i] || a[i-1] - a[i-2] != a[i] - a[i-1]){
            ans = "NO\n";
        }
    }
    cout << ans;
    return 0;
}