#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)


int N;
int x[101010];
//-----------------------------------------------------------------
string solve() {
	sort(x, x + N);

	int d = -1;
	rep(i, 1, N) {
		if (x[i - 1] == x[i]) return "NO";

		if (d < 0) {
			d = x[i] - x[i - 1];
		} else {
			if (d != x[i] - x[i - 1]) return "NO";
		}
	}

	return "YES";
}
//-----------------------------------------------------------------
int main() {
	cin >> N;
	rep(i, 0, N) scanf("%d", &x[i]);
	cout << solve() << endl;
}