#include<iostream>
#include<vector>
#include<cmath>
#include<climits>
#include<algorithm>
#include<queue>
#include<tuple>
#include<set>
#include<map>
#include<iomanip>

using namespace std;  
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
#define rep(i,n) for(ll i=0;i<(n);i++)  
#define pii pair<int,int>
#define piii pair<int,pii>
#define mp make_pair
#define pb push_back  
#define ALL(a) (a).begin(),(a).end()
#define FST first
#define SEC second  
const int INF = (INT_MAX/2);
const ll LLINF = (LLONG_MAX/2);
const double eps = 1e-5;
const double PI = M_PI;
#define DEB cerr<<"!"<<endl
#define SHOW(a,b) cerr<<(a)<<" "<<(b)<<endl
#define SHOWARRAY(ar,i,j) REP(a,i)REP(b,j)cerr<<ar[a][b]<<((b==j-1)?((a==i-1)?("\n\n"):("\n")):(" "))

int main(){
  int n; cin >> n;
  vi x(n);
  rep(i,n) cin >> x[i];
  
  sort(ALL(x));
  
  int d = x[1] - x[0];
  if(d == 0){cout << "NO" << endl; return 0;}
  
  rep(i,n-1){
    if(x[i+1] - x[i] != d) {cout << "NO" << endl; return 0;}
  }
  cout << "YES" << endl;
  
  return 0;
}