#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {
    
    int N;
    cin >> N;
    vector<long long> X(N);
    for ( int i = 0; i < N; i++ ) {
        cin >> X[i];
    }
    sort( X.begin(), X.end() );
    
    bool is_ok = true;
    long long d = 0;
    for ( int i = 1; i < N; i++ ) {
        if ( X[i] == X[i-1] ) { is_ok = false; break; }
        if ( !d  ) { d = X[i] - X[i-1]; }
        else if ( d != X[i] - X[i-1] ) { is_ok = false; break; }
    }
    
    cout << ( is_ok ? "YES" : "NO" ) << endl;
    
    return 0;
}