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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<pair<int,int>> a(n);
    for(auto &&[x, y] : a) cin >> x >> y;
    auto f = [&](int i, int j){
        auto [x1, y1] = a[i];
        auto [x2, y2] = a[j];
        return (mint)x1 * y2 - (mint)x2 * y1;
    };
    mint ans;
    for(int i = 0; i < n; i++) ans += f(i, i + 1 == n ? 0 : i + 1);
    cout << (ans / 2).val() << '\n';
}