#include <bits/stdc++.h>
using namespace std;
#define rep(i, x, limit) for (long long i = (long long)x; i < (long long)limit; i++)
#define REP(i, x, limit) for (long long i = (long long)x; i <= (long long)limit; i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define el '\n'
#define spa " "
#define Yes cout << "Yes" << el
#define No cout << "No" << el
#define YES cout << "YES" << el
#define NO cout << "NO" << el
#define eps (1e-10)
#define Equals(a,b) (fabs((a) - (b)) < eps )
#define debug(x) cerr << #x << " = " << x << el
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vs = vector<string>;
using vb = vector<bool>;
const double pi = 3.141592653589793238;
const int inf = 1073741823;
const ll infl = 1LL << 60;
const string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string abc = "abcdefghijklmnopqrstuvwxyz";
const ll MOD = 998244353;
#include<atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using vm = vector<mint>;

vector<long long> fact, invf;

// a^e mod を繰り返し二乗法で計算
long long modpow(long long a, long long e) {
    long long r = 1;
    while (e > 0) {
        if (e & 1) r = r * a % MOD;
        a = a * a % MOD;
        e >>= 1;
    }
    return r;
}

// 0! から N! までの fact, invf を前計算
void init_factorials(int N) {
    fact.assign(N+1, 1);
    rep(i,0, N) fact[i+1] = fact[i] * (i+1) % MOD;
    invf.assign(N+1, 1);
    // invf[N] = (N!)^{-1} mod
    invf[N] = modpow(fact[N], MOD-2);
    for (int i = N; i > 0; --i) {
        invf[i-1] = invf[i] * i % MOD;
    }
}

// nCk mod を O(1) で返す
long long comb(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n] * (invf[k] * invf[n-k] % MOD) % MOD;
}


int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll k;cin>>k;
  ll t=0;
  vector<pll> S;
  rep(i,0,k){
    ll l,m;cin>>l>>m;
    t+=l*m;
    S.push_back({l,m});
  }
  init_factorials(t);
  mint ans=1;
  for(auto [l,m]:S){
    ll nt=l*m;
    ans*=comb(t,nt);
    t-=l*m;
    rep(i,0,m){
      ans*=comb(nt-1,l-1);
      nt-=l;
    }
  }
  cout<<ans.val()<<el;
}