#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
#include <cstring>
#include <numeric>
#include <algorithm>
#include <functional>
#include <array>
#include <map>
#include <queue>
#include <limits.h>
#include <stack>

using namespace std;

#define Getsign(n) ((n > 0) - (n < 0))
#define QWERTYR(c) (c == 'y' || c == 'u' || (c >= 'h' && c <= 'p') ?	true : false)
map<string, int> roma_time = { { "I",1 },{ "II",2 },{ "III",3 },{ "IIII",4 },{ "V",5 },{ "VI",6 },{ "VII",7 },{ "VIII",8 },{ "IX",9 },{ "X",10 },{ "XI",11 },{ "XII",12 } };

typedef vector<int> Ivec;
typedef pair<int, int> pii;

int main() {
	int n;
	priority_queue<int> road;
	scanf("%d", &n);

	for (int i = 0; n > i; i++) {
		int a;
		scanf("%d", &a);
		road.push(a);
	}
	int kankaku,before = road.top();
	road.pop();
	kankaku = road.top() - before;

	while(!road.empty()){
		if (road.top() - before != kankaku || before == road.top()) {
			printf("NO\n");
			return 0;
		}

		before = road.top();
		road.pop();
	}
	printf("YES\n");
	return 0;
}