# coding=utf-8:
import collections

n = int(input())
line = list(map(int, input().split()))

line.sort()

c = collections.Counter(line)
d = c.values()

i = 0
k = list()

while i != len(line) - 1:
    k.append(line[i+1] - line[i])
    i += 1

if max(d) >= 2:
    print("NO")
elif k.count(k[0]) != len(k):
    print("NO")
else:
    print("YES")