// macros
#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <map>

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;

#define LLINF 1000000000000000000LL
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define debug(a) cout << "L(" << __LINE__ << "):" << #a << ":" << a << endl;

// problems limits
#define MAX_N 100000

// Variables
int N;
int X[MAX_N];

string R[12] = {"XII","I","II","III","IIII","V","VI","VII","VIII","IX","X","XI"};

// problems input
void input()
{
    cin >> N;
    FOR(i,0,N) {
        cin >> X[i];
    }
}

// problems main
void solve()
{
    sort(X,X+N);
    int x=X[0],intvl=X[1]-X[0];
    bool flg = intvl!=0;
    FOR(i,2,N) {
        flg &= (X[i]-X[i-1] == intvl);
    }
    if (flg) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}

int main()
{
    ios::sync_with_stdio(false);

    input();

    solve();
}