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

using ll = long long;
static constexpr int MOD = 998244353;

static inline ll modpow(ll a, ll e) {
    ll r = 1 % MOD;
    a %= MOD;
    while (e > 0) {
        if (e & 1) r = (r * a) % MOD;
        a = (a * a) % MOD;
        e >>= 1;
    }
    return r;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int K;
    cin >> K;

    vector<int> L(K), M(K);
    ll N = 0;
    for (int i = 0; i < K; i++) {
        cin >> L[i] >> M[i];
        N += (ll)L[i] * (ll)M[i];
    }
    // 制約で N <= 1e8
    int Nint = (int)N;

    // 必要な階乗の引数だけ集める
    vector<int> need;
    need.reserve(2 * K + 2);
    need.push_back(0);
    need.push_back(Nint);
    for (int i = 0; i < K; i++) {
        need.push_back(L[i]);
        need.push_back(M[i]);
    }
    sort(need.begin(), need.end());
    need.erase(unique(need.begin(), need.end()), need.end());

    // factorial 値を必要な点だけ保持
    unordered_map<int, int> fact;
    fact.reserve(need.size() * 2);
    fact[0] = 1;

    ll cur = 1;
    int p = 1; // need[0]=0 はセット済み
    for (int x = 1; x <= Nint; x++) {
        cur = (cur * x) % MOD;
        while (p < (int)need.size() && need[p] == x) {
            fact[x] = (int)cur;
            p++;
        }
    }

    // factorial の逆元をキャッシュ（必要な分だけ）
    unordered_map<int, int> invfact;
    invfact.reserve(need.size() * 2);

    auto get_inv_fact = [&](int x) -> ll {
        auto it = invfact.find(x);
        if (it != invfact.end()) return it->second;
        ll inv = modpow(fact[x], MOD - 2);
        invfact[x] = (int)inv;
        return inv;
    };

    // 答え = N! / ∏ ( (L_i!)^{M_i} * (M_i)! )
    ll ans = fact[Nint];

    for (int i = 0; i < K; i++) {
        ans = ans * get_inv_fact(M[i]) % MOD;                 // / (M_i)!
        ll invL = get_inv_fact(L[i]);                         // (L_i!)^{-1}
        ans = ans * modpow(invL, (ll)M[i]) % MOD;             // / (L_i!)^{M_i}
    }

    cout << ans % MOD << '\n';
    return 0;
}