#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(int i=0; i<int(n); i++)
const i64 INF = 1001001001001001001;
template<typename A> void chmin(A& l, const A& r){ if(r < l) l = r; }
template<typename A> void chmax(A& l, const A& r){ if(l < r) l = r; }
using namespace std;
#include <atcoder/modint>
using Modint = atcoder::static_modint<998244353>;

void testcase(){
    i64 K; cin >> K;
    Modint q = 1;
    Modint p = 1;
    i64 cnt = 0;
    rep(i,K){
        i64 l,m; cin >> l >> m;
        Modint x = 1;
        rep(i,l) x *= Modint::raw(i+1);
        x = x.pow(m);
        rep(i,m) x *= Modint::raw(i+1);
        q *= x;
        cnt += l * m;
    }
    rep(i,cnt) p *= Modint::raw(i+1);
    cout << (p/q).val() << "\n";
}

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    testcase();
    return 0;
}