n = int(input())

s = list(map(int, input().split()))
s = list(set(s))
s.sort()

if len(s) == 1:
    print('NO')
else:
    d = []
    for i in range(len(s)-1):
        diff = s[i+1] - s[i]
        d.append(diff)
    d = set(d)
    if len(d) == 1:
        print('YES')
    else:
        print('NO')