#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for(int i=0;i<n;i++)
#define all(A) A.begin(),A.end()

#include<atcoder/modint>
using namespace atcoder;

using mint = modint998244353;
vector<mint> fact, factinv, inv;
const ll mod = 998244353;
void prenCkModp(ll n) {
    fact.resize(n + 5);
    factinv.resize(n + 5);
    inv.resize(n + 5);
    fact[0] = fact[1] = 1;
    factinv[0] = factinv[1] = 1;
    inv[1] = 1;
    for (ll i = 2; i < n + 5; i++) {
        fact[i] = (fact[i - 1] * i);
        inv[i] = mod - (inv[mod % i] * (mod / i));
        factinv[i] = (factinv[i - 1] * inv[i]);
    }

}

mint nCk(ll n, ll k) {
    if (n < k||k<0) return 0;
    return fact[n] * (factinv[k] * factinv[n - k]);
}

int main() {

    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    ll K;
    cin>>K;

    vector<ll> L(K),M(K);
    ll S=0;
    rep(i,K){
        cin>>L[i]>>M[i];
        S+=L[i]*M[i];
    }
    int l=0;
    mint an=1,bn=1;
    map<ll,ll> U;
    ll m=0;
    rep(k,K){
        U[M[k]]++;
        m=max(m,M[k]);
    }
    for(int i=1;i<=S;i++){
        an*=i;
        if(i<=m){
            if(U.count(i))bn*=mint(an).pow(U[i]);
        }
        if(l<K&&L[l]==i){
            mint p=mint(an).pow(M[l]);
            l++;
            bn*=p;
        }
    }
    an*=bn.inv();
    cout<<an.val()<<endl;

}