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

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

#include <atcoder/modint>
using mint = atcoder::modint998244353;

int main() {
    int n; cin >> n;

    auto acc = vec<mint>(uns, n + 1);
    acc[0] = 0;

    auto t = vec<int64_t>(uns, n);
    auto v = vec<int>(uns, n);
    for (int i = 0; i < n; ++i) {
        cin >> t[i] >> v[i];
        acc[i + 1] = acc[i] + t[i];
    }

    mint ans = 0;
    for (int i = 0; i < n; ++i) {
        mint c = t[i] - 1;
        mint b = acc[i];
        mint r = acc[n] - b;
        mint p = b + 1;

        mint sub = 0;
        sub += (c + 1) * (p * p * r + p * r);
        sub += (c * (c + 1) / 2) * (-p * p + 2 * p * r - p + r);
        sub += (c * (c + 1) * (2 * c + 1) / 6) * (-2 * p + r - 1);
        sub += ((c * (c + 1) / 2) * (c * (c + 1) / 2)) * (-1);
        sub *= v[i];
        sub /= 2;

        ans += sub;
    }

    cout << ans.val() << endl;
}