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

using namespace std;

int main()
{
    uint64_t N;
    cin >> N;
    vector<uint64_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];
    }

    vector<uint64_t> A(sizeA);
    uint64_t sumA = 0;
    uint64_t index = 0;
    for (uint64_t i = 0; i < N; i++)
    {
        for (uint64_t j = 0; j < T[i]; j++)
        {
            A[index] = V[i];
            sumA += V[i];
            index++;
        }
    }

    uint64_t sum = 0;
    for (uint64_t i = 0; i < sizeA; i++)
    {
        uint64_t coef = ((i + 1) * (i + 2) / 2) * (sizeA - i);

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

    cout << sum << endl;

    return 0;
}