#include <bits/stdc++.h>

#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
using ll = long long;


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());

    bool ok = true;
    int d = x[1] - x[0];
    for(int i = 1; i < n; i++){
        if(d == 0) ok = false;
        else if(d != x[i] - x[i-1]) ok = false;
    }

    if(ok) cout << "YES" << endl;
    else cout << "NO" << endl;
}