#include <bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
#define MOD 1000000007
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3f
#define EPS (1e-10)
using namespace std;
typedef long long ll;
typedef pair<int,int>P;

int x[200000];
signed main(){
	int n;scanf("%d",&n);
	rep(i,n)scanf("%d",&x[i]);
	sort(x,x+n);
	int c=x[1]-x[0];
	if(c==0){
		puts("NO");return 0;
	}
	rep(i,n-1){
		if(x[i+1]-x[i]!=c){
			puts("NO");return 0;
		}
	}
	puts("YES");
}