N=int(input())
X=input().split(' ')


for i in range(N):
    X[i]=int(X[i])

Y=[]
for i in range(N):
    Y.append(max(X))
    X.remove(max(X))


S=[]
for i in range(N-1):
    d=Y[i+1]-Y[i]
    S.append(d)

S=list(set(S))#重複要素の削除
if(len(S)!=1):
   print('NO')

elif(int(S[0])==0):
   print('NO')

else:
   print('YES')