// https://onlinejudge.u-aizu.ac.jp/courses/library/4/CGL/all
// 3_A, 3_B, 3_C

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

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

using Point = complex<mint>;
using Polygon = vector<Point>;

struct Line {
    Point a, b;
    Line(Point a, Point b) : a(a), b(b) {}
};

struct Segment : Line {
    Segment(Point a, Point b) : Line(a, b) {}
};

// 内積
mint dot(const Point &a, const Point &b) {
    return (a.real() * b.real() + a.imag() * b.imag());
}

// 外積
mint cross(const Point &a, const Point &b) {
    return (a.real() * b.imag() - a.imag() * b.real());
}

int main() {
    int N;
    cin >> N;
    Polygon poly(N);
    for (int i = 0; i < N; i++) {
        int x, y;
        cin >> x >> y;
        poly[i] = Point(x, y);
    }
    mint ans = 0;
    for (int i = 0; i < N; i++) {
        ans += cross(poly[i], poly[(i + 1) % N]);
    }
    ans /= 2;
    cout << ans.val() << endl;
}