缺省源

#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using db = double;
using ld = long double;

#define fi first
#define se second

template <typename T> inline void read(T &x){
    x = 0;
    int r = 1;
    char ch = getchar();
    while(!isdigit(ch)) {if (ch == '-') r = -1; ch = getchar();}
    while(isdigit(ch)) x = (x << 3) + (x << 1) + ch - '0', ch = getchar();
    x *= r;
}

template <typename T> inline void write(T x) {
	if (x < 0) putchar('-'), x = -x;
	if (x > 9) write(x / 10);
	putchar(x % 10 + '0');	
}

const int mod = 998244353;

int add(int a, int b) {
    return (a + b >= mod) ? (a + b - mod) : (a + b);
}

int sub(int a, int b) {
    return add(a, mod - b);
}

int times(int a, int b) {
    return a * b % mod;
}