// ギャグ。多角形の面積でOK.
#include <iostream>
#include <algorithm>
#include <complex>
#include <atcoder/modint>
#define rep(i, n) for(i = 0; i < n; i++)
#define int long long
using namespace std;
using namespace atcoder;
using mint = modint998244353;
typedef complex<double> Point;

int n;
Point ps[100];

int cross(Point a, Point b) {
	return a.real() * b.imag() - a.imag() * b.real();
}

signed main() {
	int i;

	cin >> n;
	rep(i, n) {
		double x, y;
		cin >> x >> y;
		ps[i] = Point(x, y);
	}

	int area = 0;
	rep(i, n) {
		area += cross(ps[i], ps[(i + 1) % n]);
	}

	cout << (mint(area) / mint(2)).val() << endl;
	return 0;
}