#include <bits/stdc++.h>
#define rep(i, p, n) for (ll i = p; i < (ll)(n); i++)
#define rep2(i, p, n) for (ll i = p; i >= (ll)(n); i--)
using namespace std;
using ll = long long;
using ld = long double;
const double pi = 3.141592653589793;
const long long inf = 2 * 1e9;
const long long linf = 4 * 1e18;
const ll mod1 = 1000000007;
const ll mod2 = 998244353;
template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return 1;
    }
    return 0;
}

// atcoder
#include <atcoder/all>
using namespace atcoder;
using mint1 = modint1000000007;
using mint2 = modint998244353;

vector<pair<ll, ll>> base = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};

template <typename T>
struct area
{
    vector<pair<T, T>> point;

    T calc()
    {
        T res = 0;
        pair<T, T> A, B, C;
        A = point.at(0);
        rep(i, 0, point.size())
        {
            B = point.at(i);
            C = point.at((i + 1) % point.size());
            T temp = 0;
            temp += A.first * B.second;
            temp += B.first * C.second;
            temp += C.first * A.second;
            temp -= B.first * A.second;
            temp -= C.first * B.second;
            temp -= A.first * C.second;
            res += temp / 2;
        }
        return res;
    }
};

int main()
{

    //////////////////
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    //////////////////

    ll N;
    cin >> N;
    area<mint2> A;
    rep(i, 0, N)
    {
        ll x, y;
        cin >> x >> y;
        A.point.push_back({x, y});
    }
    cout << A.calc().val();
}