#include<iostream>
#include<vector>
#include<algorithm>
#include<cassert>
#define rep(i,n) for(i=0;i<(int)(n);i++)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;

int n;

int main(){
    int i,j;
    scanf("%d",&n);
    vector<int> x(n);
    rep(i,n)scanf("%d",&x[i]);
    sort(x.begin(),x.end());
    rep(i,n-2){
        if(x[i]+x[i+2]!=2*x[i+1]){
            puts("NO");
            return 0;
        }
    }
    printf("%s\n",x[0]==x[1]?"NO":"YES");
    return 0;
}