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

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

using mint = atcoder::modint998244353;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int k;
    cin >> k;
    vector<int> l(k), m(k);
    int n = 0;
    rep(i, k) {
        cin >> l[i] >> m[i];
        n += l[i] * m[i];
    }
    
    vector<int> num;
    num.emplace_back(n);
    rep(i, k) {
        num.emplace_back(l[i]);
        num.emplace_back(m[i]);
    }
    sort(ALL(num));
    num.erase(unique(ALL(num)), num.end());
    map<int, mint> Fac;
    Fac[0] = Fac[1] = 1;
    mint now = 1;
    int cur = 0;
    while (num[cur] < 2) {
        cur++;
    }
    for (int i = 2; i <= n; i++) {
        now *= mint(i);
        if (cur < (int)num.size() && num[cur] == i) {
            Fac[i] = now;
            cur++;
        }
    }
    
    mint ans = 1;
    ans *= Fac[n];
    rep(i, k) {
        mint x = Fac[l[i]];
        x = x.pow(m[i]);
        ans /= x;
        ans /= Fac[m[i]];
    }
    cout << ans.val() << "\n";
}