#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a;i < n;i++)
#define per(i,n,a) for (int i = n-1;i >= a;i--)
using namespace std;

int main() {
    int n; cin >> n;
    vector<int> x(n);
    rep(i,0,n) cin >> x[i];
    sort(x.begin(),x.end());
    int sa = x[1] - x[0];
    if(sa == 0){
        printf("NO\n");
        return 0;
    }
    rep(i,1,n-1){
        if(sa !=x[i+1] - x[i]){
            printf("NO\n");
            return 0;
        }
    }
    printf("YES\n");
    return 0;
}