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

#include <atcoder/all>
using namespace atcoder;

using mint = modint998244353;
using vm = vector<mint>;
using vvm = vector<vm>;
inline ostream &operator<<(ostream &os, const mint x)
{
    return os << x.val();
};
inline istream &operator>>(istream &is, mint &x)
{
    long long v;
    is >> v;
    x = v;
    return is;
};

struct Fast
{
    Fast()
    {
        std::cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << setprecision(10);
    }
} fast;

#define all(a) (a).begin(), (a).end()
#define contains(a, x) ((a).find(x) != (a).end())
#define rep(i, a, b) for (int i = (a); i < (int)(b); i++)
#define rrep(i, a, b) for (int i = (int)(b) - 1; i >= (a); i--)
#define YN(b) cout << ((b) ? "YES" : "NO") << "\n";
#define Yn(b) cout << ((b) ? "Yes" : "No") << "\n";
#define yn(b) cout << ((b) ? "yes" : "no") << "\n";

template <typename mint>
struct factorial
{
    vector<mint> f, g, h;
    factorial(int MAX = 0)
    {
        f.resize(1, mint{1});
        g.resize(1, mint{1});
        h.resize(1, mint{1});
        if (MAX > 0)
            extend(MAX + 1);
    }
    void extend(int m = -1)
    {
        int n = f.size();
        if (m == -1)
            m = n * 2;
        if (n >= m)
            return;
        f.resize(m);
        g.resize(m);
        h.resize(m);
        for (int i = n; i < m; i++)
            f[i] = f[i - 1] * mint(i);
        g[m - 1] = f[m - 1].inv();
        h[m - 1] = g[m - 1] * f[m - 2];
        for (int i = m - 2; i >= n; i--)
        {
            g[i] = g[i + 1] * mint(i + 1);
            h[i] = g[i] * f[i - 1];
        }
    }
    mint fact(int i)
    {
        if (i < 0)
            return mint(0);
        while (i >= (int)f.size())
            extend();
        return f[i];
    }
    mint fact_inv(int i)
    {
        if (i < 0)
            return mint(0);
        while (i >= (int)g.size())
            extend();
        return g[i];
    }
    mint inv(int i)
    {
        if (i < 0)
            return -inv(-i);
        while (i >= (int)h.size())
            extend();
        return h[i];
    }
    mint binom(int n, int r)
    {
        if (n < 0 || n < r || r < 0)
            return mint(0);
        return fact(n) * fact_inv(n - r) * fact_inv(r);
    }
    mint multinom(const vector<int> &r)
    {
        int n = 0;
        for (auto &x : r)
        {
            if (x < 0)
                return mint(0);
            n += x;
        }
        mint res = fact(n);
        for (auto &x : r)
            res *= fact_inv(x);
        return res;
    }
    mint binom_naive(int n, int r)
    {
        if (n < 0 || n < r || r < 0)
            return mint(0);
        mint ret = mint(1);
        r = min(r, n - r);
        for (int i = 1; i <= r; ++i)
            ret *= inv(i) * (n--);
        return ret;
    }
    mint P(int n, int r)
    {
        if (n < 0 || n < r || r < 0)
            return mint(0);
        return fact(n) * fact_inv(n - r);
    }
    mint H(int n, int r)
    {
        if (n < 0 || r < 0)
            return mint(0);
        return r == 0 ? 1 : binom(n + r - 1, r);
    }
};

void solve()
{
    int n;
    cin >> n;
    vector<pair<int, int>> lm(n);
    int s = 0;
    rep(i, 0, n)
    {
        int l, m;
        cin >> l >> m;
        lm[i] = {l, m};
        s += l * m;
    }

    mint ans = 1;
    for (auto [l, m] : lm)
    {
        mint f = 1;
        rep(i, 0, l) f *= i + 1;
        ans *= f.pow(m);
        f = 1;
        rep(i, 0, m) f *= i + 1;
        ans *= f;
    }
    ans = ans.inv();
    rep(i, 0, s) ans *= i + 1;
    cout << ans << "\n";
}

int main()
{
    int t = 1;
    // cin >> t;
    while (t--)
        solve();
}