#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int N;

int main(){
    while(cin >> N){
        vi x(N);
        rep(i, N)scanf("%d", &x[i]);

        sort(all(x));
        int d = x[1] - x[0];
        int ok = 1;
        ok &= d != 0;
        rep(i, N - 1)ok &= x[i + 1] - x[i] == d;
        puts(ok ? "YES" : "NO");
    }
}