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

sorted_x = sorted(x)

delta = sorted_x[1] - sorted_x[0]

flag = 1

if delta == 0:
    flag = 0
else:
    for i in range(n-1):
        if delta != sorted_x[i+1] - sorted_x[i]:
            flag = 0
            break
        
if flag == 1:
    print('YES')
else:
    print('NO')