#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N; cin >> N;
    vector<int> x(N);
    rep(i,N) cin >> x[i];

    sort(x.begin(), x.end());
    x.erase(unique(x.begin(), x.end()), x.end());

    if(int(x.size()) != N) { cout << "NO" << endl; return 0; }
    rep(i,N-1) {
        if(x[i + 1] - x[i] != x[1] - x[0]) {
            cout << "NO" << endl;
            return 0;
        }
    }

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