func_code_string: /*   西江月·证明   即得易见平凡，仿照上例显然；留作习题答案略，读者自证不难。   反之亦然同理，推论自然成立；略去过程Q.E.D.，由上可知证毕。      result of thinking: Pure.    主要是非内、外向树的情形容易遗漏.       AC:   */   #include <bits/stdc++.h>   using namespace std;   typedef long long ll;   typedef unsigned long long ull;   typedef long double ldouble;   template<class T> bool chmin(T &x, const T &y) {     return x > y ? (x = y, true) : false;   }   template<class T> bool chmax(T &x, const T &y) {     return x < y ? (x = y, true) : false;   }      #define maxn 1000005   const ll mod = 998244353;   const ll inv2 = 499122177;   const ll inv6 = 166374059;   int n;   ll f[maxn], r[maxn], df[maxn];      int main() {     scanf( %d , &n);     f[0] = r[0] = 1;     for (int i = 1; i <= n; i++) {       f[i] = (f[i - 1] * f[i - 1] % mod * inv2 + 3 * f[i - 1] * inv2 + 1) % mod;       r[i] = (f[i] + (f[i - 1] * f[i - 1] % mod * f[i - 1]                       + f[i - 1] * f[i - 1] * 3                       + f[i - 1] * 2) % mod * inv6) % mod;     }     ll ans = ((r[n] - r[n - 1]) * 2 - 1) % mod;     df[0] = f[0];     for (int i = 1; i <= n; i++)       df[i] = f[i] - f[i - 1];     for (int i = 1; i <= n - 2; i++) {       (ans += (df[i] - df[i - 1]) * (df[n - 1 - i] - 1)) %= mod;     }     printf( %lld n , (ans + mod) % mod);     return 0;   }   