def main():
    N = int(input())
    X = tuple(map(int, input().split()))

    x = sorted(X)
    l = x[1] - x[0]
    if l == 0:
        print('NO')
        return

    for i in range(1, N):
        if x[i] - x[i-1] != l:
            ans = 'NO'
            break
    else:
        ans = 'YES'

    print(ans)

main()