#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <cassert>
using namespace std;

#define GET_ARG(a,b,c,F,...) F
#define REP3(i,s,e) for (i = s; i <= e; i++)
#define REP2(i,n) REP3 (i,0,(int)(n)-1)
#define REP(...) GET_ARG (__VA_ARGS__,REP3,REP2) (__VA_ARGS__)
#define RREP3(i,s,e) for (i = s; i >= e; i--)
#define RREP2(i,n) RREP3 (i,(int)(n)-1,0)
#define RREP(...) GET_ARG (__VA_ARGS__,RREP3,RREP2) (__VA_ARGS__)
#define DEBUG(x) cerr << #x ": " << x << endl

int x[100000];

int main(void) {
    int i, n;
    scanf("%d",&n);
    REP (i,n) cin >> x[i];
    sort(x,x+n);
    int dis = x[1] - x[0];
    if (dis == 0) {
        cout << "NO" << endl;
        return 0;
    }
    REP (i,n-1) if (x[i+1] - x[i] != dis) {
        cout << "NO" << endl;
        return 0;
    }
    cout << "YES" << endl;
    return 0;
}