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

#define int long long
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define all(v) (v).begin(),(v).end()
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define pb push_back
#define mp make_pair
#define fi first
#define se second
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

signed main(){
    int n;cin>>n;
    vint v(n);rep(i,n)cin>>v[i];

    sort(all(v));
    bool ok=true;
    for(int i=0;i+1<v.size();i++)if(v[i+1]-v[i]!=v[1]-v[0])ok=false;
    if(v[0]==v[1])ok=false;

    if(ok)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}