#include <iostream>
#include <iomanip>
#include <cassert>
#include <vector>
#include <algorithm>
#include <utility>
#include <numeric>
#include <tuple>
#include <ranges>
#include <random>
// #include "Src/Number/IntegerDivision.hpp"
// #include "Src/Utility/BinarySearch.hpp"
// #include "Src/Sequence/CompressedSequence.hpp"
// #include "Src/Sequence/RunLengthEncoding.hpp"
// #include "Src/Algebra/Group/AdditiveGroup.hpp"
// #include "Src/DataStructure/FenwickTree/FenwickTree.hpp"
// #include "Src/DataStructure/SegmentTree/SegmentTree.hpp"
// #include "Src/DataStructure/DisjointSetUnion/DisjointSetUnion.hpp"
namespace zawa {}
using namespace zawa;
// #include "atcoder/modint"
// using mint = atcoder::modint998244353;
// #include <array>
// #include <bit>
// #include <bitset>
// #include <climits>
// #include <cmath>
// #include <set>
// #include <unordered_set>
// #include <map>
// #include <unordered_map>
// #include <optional>
// #include <queue>
// #include <stack>
// #include <deque>
// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
using namespace std;
template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    for (int i = 0 ; i < ssize(v) ; i++)
        os << v[i] << (i + 1 == ssize(v) ? "" : " ");
    return os;
}
int main() {
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(20);
#if !defined DEBUG
    int N;
    cin >> N;
    vector<pair<int, int>> P(N);
    for (auto& [x, y] : P)
        cin >> x >> y;
    P.push_back(P[0]);
    long long ans = 0;
    for (int i = 0 ; i < N ; i++) {
        auto [x1, y1] = P[i];
        auto [x2, y2] = P[i + 1];
        ans += (long long)x1 * y2 - (long long)x2 * y1;
    }
    ans %= 998244353;
    ans = (ans * 499122177) % 998244353;
    cout << ans << '\n';
#else
    mt19937 mt{random_device{}()};
    for (int testcase = 0 ; ; ) {
        cerr << "----------" << ++testcase << "----------" << endl;
        
        auto a = solve(), b = naive();
        if (a != b) {
            // print testcase

            cerr << "you: " << a << endl;
            cout << "correct: " << b << endl;
            exit(0);
        }
    }
#endif
}