打表找规律，发现1-n每个数的价值为等差数列，且第一个非零数为3-n的累乘

#include <bits/stdc++.h>
#define int long long
using namespace std;
using ll = long long;
using pii = pair<int, int>;

const int mod = 998244353;

signed main() {
    ios::sync_with_stdio(false), cin.tie(nullptr);
    int n;
    cin >> n;
    int topval = 1;
    int res = 0;
    for (int i = 3; i <= n; i ++ ) topval = (topval * i % mod) % mod;
    for (int i = 2, val = topval; i <= n; i ++) {
        res = (res + val) % mod;
        val =  (val + topval) % mod;
    }
    cout << (res % mod + mod) % mod << endl;
    return 0;
}