N = int(input())
X = list(map(int, input().split(' ')))
X.sort()
flag = True
diff = X[1] - X[0]
for i in range(1, N - 1):
    if X[i+1] - X[i] != diff or diff == 0:
        flag = False

if flag:
    print("YES")
else:
    print("NO")