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

int main() {
    int N;
    cin >> N;
    vector<int> x(N+1);
    REP(i,N) cin >> x[i];
    sort(x.begin(),x.end());
    int d = x[1]-x[0];
    for(int i = 1; i < N; i++){
        if(x[i]-x[i-1] != d || x[i]-x[i-1] == 0){
            cout << "NO" << endl;
            exit(0);
        }
    }
    cout << "YES" << endl;
    return 0;
}