#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
static const int INF = 0x3f3f3f3f; static const long long INFL = 0x3f3f3f3f3f3f3f3fLL;
typedef vector<int> vi; typedef pair<int, int> pii; typedef vector<pair<int, int> > vpii; typedef long long ll;
template<typename T, typename U> static void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> static void amax(T &x, U y) { if(x < y) x = y; }

int main() {
	int N;
	while(~scanf("%d", &N)) {
		vector<int> x(N);
		for(int i = 0; i < N; ++ i)
			scanf("%d", &x[i]);
		sort(x.begin(), x.end());
		int d = x[1] - x[0];
		bool ok = d != 0;
		rep(i, N - 1)
			ok &= x[i + 1] - x[i] == d;
		puts(ok ? "YES" : "NO");
	}
	return 0;
}