#include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repp(i, n) rep(i, 0, n)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define int long long
using namespace std;

signed main(){
    int n;
    cin >> n;
    vector<int> x(n);
    rep(i, 0, n) cin >> x[i];
    sort(all(x));
    bool f = true;
    int d = x[1] - x[0];
    rep(i, 2, n){
        if(x[i] - x[i - 1] != d) f = false;
    }
    if(f && d != 0) cout << "YES" << endl;
    else cout << "NO" << endl;
}