#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int x[n];
    for(int i = 0; i < n; i++)
        cin >> x[i];
    
    sort(x,x+n);

    int flag = 0;
    for(int i = 0; i < n - 2; i++){
        if(x[i+1] - x[i] != x[i+2] - x[i+1] || x[1] - x[0] == 0){
            flag = 1;
            break;
        }
    }

    cout << (flag == 0 ? "YES" : "NO") << endl;

    return 0;
}