#include<bits/stdc++.h>
// #include<atcoder/all>
// #include<boost/multiprecision/cpp_int.hpp>

using namespace std;
// using namespace atcoder;
// using bint = boost::multiprecision::cpp_int;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<ll,ll>;
using vi = vector<ll>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using ve = vector<vector<int>>;
using vb = vector<bool>;
using vvb = vector<vb>;
#define rep(i,s,n) for(ll i = (ll)s;i < (ll)n;i++)
#define ALL(x) (x).begin(),(x).end()
#define sz(c) ((ll)(c).size())
#define LB(A,x) (int)(lower_bound(A.begin(),A.end(),x)-A.begin())
#define UB(A,x) (int)(upper_bound(A.begin(),A.end(),x)-A.begin())
// #define MOD 1000000007
#define MOD 998244353
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
template<typename T>ostream&operator<<(ostream&os,vector<T>&v){for(int i = 0;i < v.size();i++)os<<v[i]<<(i+1!=v.size()?" ":"");return os;}
template<typename T>istream&operator>>(istream&is,vector<T>&v){for(T&in:v)is>>in;return is;}
template<typename T1,typename T2>ostream&operator<<(ostream&os,pair<T1,T2>&p){os<<p.first<<" "<<p.second;return os;}
template<typename T1,typename T2>istream&operator>>(istream&is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T> inline bool chmax(T &a,T b){if(a < b){a = b;return true;}return false;}
template<typename T> inline bool chmin(T &a,T b){if(a > b){a = b;return true;}return false;}
ld dist(ld x1,ld y1,ld x2, ld y2){return sqrtl((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}

class Comb{
  public:
  const int n;
  // const int mod = 1000000007;
  const int mod = 998244353;
  vector<int> fac,refac;
  Comb(int N) : n(N),fac(N+1,1),refac(N+1,1) {
    for(int i = 0;i < n;i++)fac[i+1] = 1ll*fac[i]*(i+1)%mod;
    refac[n] = modpow(fac[n],mod-2);
    for(int i = n;i > 0;i--)refac[i-1] = 1ll*refac[i]*i%mod;
  }
  long long comb(long long n,long long r){
    if(n < r)return 0;
    long long res = 1ll*fac[n]*refac[r]%mod;
    res = res*refac[n-r]%mod;
    return res;
  }
  long long modpow(long long n,long long r){
    long long res = 1;
    while(r){
      if(r & 1)res = res*n%mod;
      n = n*n%mod;
      r >>= 1;
    }
    return res;
  }
};
long long modpow(long long n,long long r,int mod){
  long long res = 1;
  while(r){
    if(r & 1)res = res*n%mod;
    n = n*n%mod;
    r >>= 1;
  }
  return res;
}

int main(){
  
  ios_base::sync_with_stdio(0), cin.tie(0);
  ll K;cin >> K;
  vector<int> L(K),M(K);
  rep(i,0,K)cin >> L[i] >> M[i];
  ll sm = 0;
  rep(i,0,K)sm += L[i]*M[i];
  vector<P> quo;
  rep(i,0,K){
    ll m = M[i],l = L[i];
    quo.emplace_back(l-1,m);
  }
  sort(ALL(quo));
  ll res = 1;
  rep(i,1,sm+1)res = res*i%MOD;
  ll k = 1,cnt = 1;
  rep(i,0,sz(quo)){
    while(cnt < quo[i].first)cnt++,k = k*cnt%MOD;
    res = res*modpow(modpow(k,MOD-2,MOD),quo[i].second,MOD)%MOD;
  }
  ll g = 1;
  rep(i,0,K){
    ll m = M[i],l = L[i];
    for(int j = l*m;j > 0;j -= l)g = g*j%MOD;
  }
  res = res*modpow(g,MOD-2,MOD)%MOD;
  cout << res << "\n";

  return 0;
}