N = int(input())
xs = sorted(list(map(int, input().split())))
nw = xs[1]
itv = nw - xs[0]
if itv == 0:
    print('NO')
else:
    for i in range(1, N-1):
        nxt = xs[i+1]
        if nxt - nw == itv:
            continue
        else:
            print('NO')
            break
        nw = nxt
    else:
        print('YES')