#include<bits/stdc++.h>
using namespace std;
using ll = long long;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("YES")
#define p_no() p("NO")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

void vprint(vector<ll> A){
    ll L = A.size();
    FOR(i, 0, L){
        if(i) cout << ' ';
        cout << A[i];
    }
    cout << endl;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N;
    cin >> N;

    vector<ll> A(N);
    FOR(i, 0, N){
        cin >> A.at(i);
    }
    sort(ALL(A));

    FOR(i, 0, N-1){
        if(A[i]==A[i+1]){
            p_no();
            return 0;
        }
    }

    ll diff = A[1]-A[0];
    FOR(i, 0, N-1){
        ll d = A[i+1]-A[i];
        if(d!=diff){
            p_no();
            return 0;
        }
    }
    p_yes();
    
    return 0;
}