n=int(input())
a=list(int(i) for i in input().split())

count=0
a.sort()
d=a[1]-a[0]
for i in range(len(a)-1):
    for j in range(i+1,len(a)):
        if a[i]==a[j]:
            count+=1

for i in range(len(a)-1):
    if a[i+1]-a[i]!=d:
        count+=1

if count==0:
    print('YES')
else:
    print('NO')