#include <iostream>
#include <cstdlib>
#include <vector>
#include <algorithm>
int main()
{
    int n, a;
    std::vector<int> v;
    std::cin >> n;
    for(int i = 0; i < n; i++){
        std::cin >> a;
        v.push_back(a);
    }
    std::sort(v.begin(), v.end());
    int diff = v[1] - v[0];
    if(diff == 0){
        std::cout << "NO" << std::endl;
    } else {
        for(int i = 2; i < n; i++){
            if(v[i] - v[i - 1] != diff){
                std::cout << "NO" << std::endl;
                return 0;
            }
        }
        std::cout << "YES" << std::endl;
    }
    return 0;
}