#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

int main()
{
    int n;
    cin >> n;
    vector<int> x(n);
    for(int i=0; i<n; ++i)
        cin >> x[i];
    sort(x.begin(), x.end());

    int d = x[1] - x[0];
    if(d == 0){
        cout << "NO" << endl;
        return 0;
    }

    for(int i=0; i<n-1; ++i){
        if(x[i+1] - x[i] != d){
            cout << "NO" << endl;
            return 0;
        }
    }

    cout << "YES" << endl;
    return 0;
}