n = int(input())
X = list(map(int, input().split()))

if len(X) != len(set(X)):
    print('NO')
    exit()

X.sort()
d = X[1]-X[0]
for i in range(n-1):
    if X[i]+d != X[i+1]:
        print('NO')
        exit()
else:
    print('YES')