#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
ll I=1167167167167167167;
ll Q=998244353;
#define rep(i,a) for (ll i=0;i<a;i++)
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
template<class T> void print_tate(vector<T> &v) {rep(i,v.size()) cout<<v[i]<<"\n";}
void yneos(bool a){if(a) cout<<"YES"<<"\n"; else cout<<"NO"<<"\n";}

ll jyo(ll a,ll b){
	if(b==0) return 1;
	if(b%2==0) return jyo((a*a)%Q,b/2);
	return (a*jyo(a,b-1))%Q;
}

ll A,B;

ll f(ll a){
	return (((a*(a+1))%Q)*A)%Q;
}

ll g(ll a){
	return (B*(((a*(a+1)%Q)*(2*a+1))%Q))%Q;
}

ll h(ll a){
	return (f(a)*f(a))%Q;
}

//おちこんだりもしたけれど、私はげんきです。
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	A=jyo(2,Q-2);
	B=jyo(6,Q-2);
	ll N;
	cin>>N;
	ll L=0;
	ll T[N],V[N];
	rep(i,N){
		cin>>T[i]>>V[i];
		T[i]%=Q;
		L+=T[i];
		L%=Q;
	}
	ll ans=0;

	ll X=-1,Y=-1;
	rep(i,N){
		Y+=T[i];
		ll U=((3*L-2)%Q)*((f(Y)-f(X))%Q);
		U%=Q;
		U+=((L-3)*((g(Y)-g(X))%Q))%Q;
		U%=Q;
		U+=(h(X)-h(Y))%Q;
		U%=Q;
		U+=2*L*T[i];
		U=(U%Q+Q)%Q;
		ans+=V[i]*U;
		ans%=Q;
		X+=T[i];
	}
	cout<<(ans*A)%Q<<"\n";
}