#include <bits/stdc++.h>
#include <atcoder/all>
using mint = atcoder::static_modint<998244353>;
//using mint = atcoder::static_modint<1000000007>;
using namespace std;
using namespace atcoder;
using ld = long double;
using ll = long long;
#define mp(a,b) make_pair(a,b)
#define rep(i,s,n) for(int i=s; i<n; i++)
const vector<int> dx{1,0,-1,0},dy{0,1,0,-1};

const int M=100000000;
vector<mint> factorial(M+1,1);
// vector<mint> invfactorial(M+1,1);

int main(){
    int k;cin >> k;
    int n=0;
    vector<int> l(k),r(k);
    rep(i,0,k)cin >> l[i] >> r[i],n+=l[i]*r[i];
    rep(i,1,M+1)factorial[i]=factorial[i-1]*i;
    mint ans=factorial[n];
    rep(i,0,k){
        ans/=factorial[l[i]].pow(r[i]);
        ans/=factorial[r[i]];
    }
    cout << ans.val();
}