#include "bits/stdc++.h"
using namespace std;

#include <iostream>
#include <vector>
#include <list>

using namespace std;

int main()
{
    uint64_t N;
    cin >> N;
    vector<uint32_t> T(N), V(N);
    uint64_t sizeA = 0;
    for (uint64_t i = 0; i < N; i++) {
        cin >> T[i] >> V[i];
        sizeA += T[i];
    }


    uint64_t sum = 0;
    uint64_t idx = 0;
    for (uint64_t i = 0; i < N; i++)
    {
        uint64_t coef = 0;
        for (uint64_t j = 0; j < T[i]; j++)
        {
            coef += ((idx + 1) * (idx + 2) / 2) * (sizeA - idx);
            idx++;
        }

        sum += coef * V[i];
        sum %= 998244353;
    }

    cout << sum << endl;

    return 0;
}