#include<bits/stdc++.h>
using namespace std;
#include<atcoder/modint>
typedef atcoder::modint998244353 mint;

int main() {
	int n; cin >> n;
	vector<long long> x(n), y(n);
	for (int i=0; i<n; i++) {
		cin >> x[i] >> y[i];
	}
	mint ans = 0;
	for (int i=0; i<n-2; i++) {
		long long ax = x[i+1] - x[0];
		long long bx = x[i+2] - x[0];
		long long ay = y[i+1] - y[0];
		long long by = y[i+2] - y[0];
		ans += abs(ax * by - bx * ay);
	}
	ans *= mint(2).inv();
	cout << ans.val() << endl;
}