f[0] = 0, f[1] = 1; if (f[1] >= k) ans = (ans + 1) % mod;
	for (int i = 2; i <= n; i++) {
		int r = i;
		while (r && !f[r]) r = nxt[r];
		f[i] = f[r] + 1;
		if (f[i] >= k) ans = (ans + 1) % mod;
	}

rt