#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
using mint = modint998244353;
const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int k; cin >> k;
	int sum = 0;
	mint ans = 1;
	map<int, int>mp1;
	map<int, vector<int>>mp2;
	rep(i, k) {
		int l, m; cin >> l >> m;
		sum += l * m;
		mp1[m]++;
		mp2[l].push_back(m);
		//ans *= c.ifact[l].pow(m);
		//ans *= c.ifact[m];
	}
	{
		int now = 1;
		mint fact = 1;
		for (auto[k, v] : mp1) {
			while (now != k) {
				now++;
				fact *= now;
			}
			ans *= fact.pow(v);
		}
	}

	{
		int now = 1;
		mint fact = 1;
		for (auto[k, v] : mp2) {
			while (now != k) {
				now++;
				fact *= now;
			}
			for (auto e : v) {
				ans *= fact.pow(e);
			}
		}
	}
	ans = ans.inv();
	rep2(i, 1, sum + 1)ans *= i;
	cout << ans.val() << endl;
	return 0;
}