#include <iostream>
#include <vector>
using namespace std;
using ll=long long;
using ull=unsigned long long;

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

#define rep(i, e) for(int i=0; i<(int)(e); ++i)
#define dir(dx, dy) for(auto [dx, dy]: vector{pair{1, 0}, {0, 1}, {-1, 0}, {0, -1}})

#define all(v) (v).begin(), (v).end()
#define all_r(v) (v).rbegin(), (v).rend()

#define in(i) cin >> i
#define in_d(type, i) type i; cin >> i
#define in_z(i) cin >> i; --i
#define in_d_z(type, i) type i; cin >> i; --i
#define out(i) cout << (i) << endl
#define err(i) cerr << (i) << endl
#define out_e() cout << endl
#define err_e() cerr << endl
#define out_s(i) cout << (i) << " "
#define err_s(i) cerr << (i) << " "

#define out_f(i) cout << fixed << setprecision(15) << (i) << endl
#define err_f(i) cerr << fixed << setprecision(15) << (i) << endl
#define out_fs(i) cout << fixed << setprecision(15) << (i) << " "
#define err_fs(i) cerr << fixed << setprecision(15) << (i) << " "

constexpr int max32=1'000'000'000;
constexpr ll max64=1'000'000'000'000'000'000;

template <typename T>
bool chmin(T & l, const T & r) {
    if(r<l){
        l=r;
        return true;
    }
    return false;
}
template <typename T>
bool chmax(T & l, const T & r) {
    if(r>l){
        l=r;
        return true;
    }
    return false;
}

int main(void) {
    in_d(int, k);
    vector<int> l(k);
    vector<int> m(k);
    int sum_lm=0;
    rep(i, k){
        in(l[i]);
        in(m[i]);
        sum_lm+=l[i]*m[i];
    }
    constexpr int f_max=100'000'000;
    auto fact=[](int n){
        mint res=1;
        for(int i=1;i<=n;++i){
            res*=i;
        }
        return res;
    };
    mint ans=fact(sum_lm);
    rep(i, k){
        ans/=fact(l[i]).pow(m[i]);
        ans/=fact(m[i]);
    }
    out(ans.val());
    return 0;
}