/**
	author:  shobonvip
	created: 2025.01.17 21:20:38
**/

#include<bits/stdc++.h>
using namespace std;

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)
#define all(v) v.begin(), v.end()

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}



int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	
	int k; cin >> k;
	vector<ll> l(k), m(k);
	rep(i,0,k) cin >> l[i] >> m[i];

	int cnt = 0;
	rep(i,0,k) cnt += l[i] * m[i];
	mint ans = 1;
	rep(i,1,cnt+1)ans *= i;
	rep(i,0,k) {
		mint mnt = 1;
		rep(x,1,l[i]*m[i]+1) mnt *= x;
		ans /= mnt;
		mnt = 1;
		rep(x,1,l[i]-1+1) mnt *= x;
		ans /= mnt.pow(m[i]);
		rep(x,1,m[i]*l[i])  {
			if (x % l[i] == 0) continue;
			ans *= x;
		}
		/*
		rep(j,0,m[i]) {
			ans *= fact[(j + 1) * l[i] - 1];
			ans *= factinv[j * l[i]];
		}
		*/
	}
	cout << ans.val() << endl;
}