import sys
readline=sys.stdin.readline
from collections import Counter

N=int(readline())
X=sorted(list(map(int,readline().split())))
x0=X[0]
d=X[1]-X[0]
ans="YES"
for i in range(N):
    if X[i]!=x0+d*i:
        ans="NO"
if d==0:
    ans="NO"
print(ans)