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

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