#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 100000000000000000
mint Nsum = 0;

mint f0(mint n){
	return n;
}

mint f1(mint n){
	mint ret = n;
	ret *= n+1;
	ret /= 2;
	return ret;
}

mint f2(mint n){
	mint ret = n;
	ret *= n+1;
	ret *= n*2+1;
	ret /= 6;
	return ret;
}

mint f3(mint n){
	mint ret = f1(n);
	ret *= ret;
	return ret;
}

mint get(mint n){
	
	mint ret = -f3(n);
	ret += Nsum * f2(n);
	ret += (Nsum+1) * f1(n);
	
	return ret;
	
}

mint get(mint L,mint R){
	return get(R) - get(L-1);
}

int main(){
	
	int N;
	cin>>N;
	
	vector<long long> T(N),V(N);
	
	rep(i,N){
		scanf("%lld %lld",&T[i],&V[i]);
		Nsum += T[i];
	}
	
	mint cur = 0;
	
	mint ans = 0;
	
	rep(i,N){
		ans += get(cur+1,cur+T[i]) * V[i];
		cur += T[i];
	}
	
	ans /= 2;
	
	cout<<ans.val()<<endl;
	
	
	return 0;
}