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


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




list.sort(X)


S=[]
for i in range(N-1):
    d=X[i+1]-X[i]
    S.append(d)
    S=list(set(S))#重複要素の削除
    if(len(S)!=1):
       print('NO')
       break
    elif(int(S[0])==0):
       print('NO')
       break
    elif(i==N-2):
       print('YES')