#include "bits/stdc++.h"
using namespace std;
#define fastcin {\
    cin.tie(0);\
    ios::sync_with_stdio(false);\
}
#define rep(i, a, b) for(int i = a; i < b; i++)
#define rrep(i, a, b) for(int i = a; i >= b; i--)
#define fore(i, a) for(auto &i:a)
#define print(x) cout << x << "\n"
#define SORT(a, n) sort(a, a+n);
#define REVERSE(a,n) reverse(a,a+n);
#define VSORT(v) sort(v.begin(), v.end());
#define VREVERSE(v) reverse(v.begin(), v.end());
#define MOD 1000000007
#define yes "YES"
#define no "NO"
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;

int n, diff, x[100000];
string ans = yes;
int main() {
    fastcin;
    cin >> n;
    rep(i, 0, n) cin >> x[i];
    SORT(x, n);
    diff = x[1] - x[0];
    if(diff==0) ans = no;
    else {
        rep(i, 1, n-1) {
            if((x[i+1]-x[i])!=diff) {
                ans = no;
                break;
            }
        }
    }
    print(ans);
    return 0;
}