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

//--------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define LL long long
#define INF INT_MAX/3

//--------------------------------------------
const double EPS = 1e-14;
const double PI  = acos(-1.0);

//--------------------------------------------

int main(){
  int n;
  int x[100000];

  scanf("%d",&n);
  REP (i, n) scanf("%d",&x[i]);
  sort(x,x+n);
  bool flag = true;
  int dis = x[1] - x[0];
  REP (i, n - 1) {
    if (x[i + 1] - x[i] != dis) flag = false;
    if (x[i + 1] == x[i]) flag = false;
    if (!flag) break;
  }
  if (flag) printf("YES\n");
  else printf("NO\n");
}