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

int main(){
    vector<double> V;
    int vec = 0; int intval = 0;
    int n = 0; cin >> n;
    for(int i = 0; i < n; ++i){
        cin >> vec;
        V.push_back(vec);
    }
    sort(V.begin(),V.end(), greater<int>());
    intval = V[0] - V[1];
    for(int i = 0; i < n - 1; ++i){
        if(V[i] != V[i+1]+intval || V[i] == V[i+1]){
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "YES" << endl;
    return 0;
}