#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;

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