#include <bits/stdc++.h>

#include <atcoder/modint>
using Mint = atcoder::modint998244353;
std::ostream &operator<<(std::ostream &os, const Mint &m) {
  return os << m.val();
}

#define REP_(i, a_, b_, a, b, ...) \
  for (int i = (a), END_##i = (b); i < END_##i; ++i)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
#define ALL(x) std::begin(x), std::end(x)
using i64 = long long;

template <typename T, typename U>
inline bool chmax(T &a, U b) {
  return a < b and ((a = std::move(b)), true);
}
template <typename T, typename U>
inline bool chmin(T &a, U b) {
  return a > b and ((a = std::move(b)), true);
}
template <typename T>
inline int ssize(const T &a) {
  return (int)std::size(a);
}

template <typename T>
std::istream &operator>>(std::istream &is, std::vector<T> &a) {
  for (auto &x : a) is >> x;
  return is;
}
template <typename T, typename U>
std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &a) {
  return os << "(" << a.first << ", " << a.second << ")";
}
template <typename Container>
std::ostream &print_seq(const Container &a, std::string_view sep = " ",
                        std::string_view ends = "\n",
                        std::ostream &os = std::cout) {
  auto b = std::begin(a), e = std::end(a);
  for (auto it = std::begin(a); it != e; ++it) {
    if (it != b) os << sep;
    os << *it;
  }
  return os << ends;
}
template <typename T, typename = void>
struct is_iterable : std::false_type {};
template <typename T>
struct is_iterable<T, std::void_t<decltype(std::begin(std::declval<T>())),
                                  decltype(std::end(std::declval<T>()))>>
    : std::true_type {};

template <typename T, typename = std::enable_if_t<
                          is_iterable<T>::value &&
                          !std::is_same<T, std::string_view>::value &&
                          !std::is_same<T, std::string>::value>>
std::ostream &operator<<(std::ostream &os, const T &a) {
  return print_seq(a, ", ", "", (os << "{")) << "}";
}

#ifdef ENABLE_DEBUG
#include "debug_dump.hpp"
#else
#define DUMP(...)
#endif

using namespace std;

auto solve() {
  int n;
  cin >> n;
  Mint m = 0;
  vector<pair<Mint, Mint>> tv(n);
  REP(i, n) {
    i64 t, v;
    cin >> t >> v;
    tv[i] = {Mint(t), Mint(v)};
    m += t;
  }

  auto f = [&](Mint a, Mint b) -> Mint {
    Mint res = 0;
    res += 3 * a.pow(4);
    res += a.pow(3) * (6 - 4 * m);
    res -= 3 * a.pow(2) * (4 * m + 1);
    res -= 2 * a * (4 * m + 3);
    res -= (b.pow(3) + 6 * b.pow(2) + 11 * b + 6) * (3 * b - 4 * m);
    res /= 12;
    return res;
  };

  Mint ans = 0;
  Mint S = 0;
  REP(i, n) {
    auto [t, v] = tv[i];
    Mint fi = f(S, S + t - 1);
    ans += Mint(v) * fi;
    S += t;
  }
  return ans / 2;
}

int main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  cout << solve() << "\n";
}