N = int(input())
X = list(map(int, input().split()))
X.sort()
Xsub = [X[i+1] - Xi for i, Xi in enumerate(X) if i != N-1]
toukankaku = [X == Xsub[0] for X in Xsub]

if all(toukankaku) and sum(Xsub)!=0:
    print('YES')
else:
    print('NO')