for (int k = FFMAX(n - N + i, 0); k <= FFMIN(i, n); k++) {
acc += ((fact(i) * fact(N - i)) /
(fact(k) * fact(i - k) * fact(n - k) * fact(N - i - n + k))) *
for (int k = FFMAX(n - N + i, 0); k <= FFMIN(i, n); k++) {
acc += ((fact(i) * fact(N - i)) /
(fact(k) * fact(i - k) * fact(n - k) * fact(N - i - n + k))) *