2 * n 矩形，有障碍物， 求从左上角到右下角的路径有多少种？ ``` from itertools import product n, k, l, r = tuple(map(int, input().split())) f = list(range(l, r+1)) t = tuple((f for i in range(n))) a = product(*t) res = 0 for i in a: if sum(i) % k == 0: res += 1 print(res) ```