#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second
mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());
const ll MOD1000000007 = 1000000007;
const ll MOD998244353 = 998244353;
const ll MOD[3] = {999727999, 1070777777, 1000000007};
const ll LINF = 1LL << 60LL;
const int IINF = (1 << 30) - 2;

#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;

mint combination(int n, int k){
    mint res = 1;
    for(int i=0; i<k; i++){
        res *= mint(n-i);
        res /= mint(i+1);
    }
    return res;
}

void solve(){
    int k; cin >> k;
    int n = 0;
    vector<int> l(k), m(k);
    for(int i=0; i<k; i++){
        cin >> l[i] >> m[i];
        n += l[i]*m[i];
    }

    mint ans = 1;
    for(int i=0; i<k; i++){
        for(int j=0; j<m[i]; j++){
            ans *= combination(n, l[i]);
            n -= l[i];
        }
    }

    cout << ans.val() << '\n';
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    int T=1;
    //cin >> T;
    while(T--) solve();
}