#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <array>
#include <iomanip>
#include <utility>
#include <tuple>
#include <functional>
#include <bitset>
#include <cassert>
#include <complex>
#include <stdio.h>
#include <time.h>
#include <numeric>
#include <random>
#include <unordered_set>
#include <unordered_map>
#define all(a) (a).begin(), (a).end()
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define req(i, a, b) for (ll i = (a); i < (b); i++)
#define pb push_back
#define debug(x) cerr << __LINE__ << ' ' << #x << ':' << (x) << '\n'
#define debug2(x, y) cerr << __LINE__ << ' ' << #x << ':' << (x) << ',' << #y << ':' << (y) << '\n'
#define debug3(x, y, z) cerr << __LINE__ << ' ' << #x << ':' << (x) << ',' << #y << ':' << (y) << ',' << #z << ':' << (z) << '\n'
using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef long double ld;
template<class T> using P = pair<T, T>;
template<class T> using pri_l = priority_queue<T>;
template<class T> using pri_s = priority_queue<T, vector<T>, greater<T>>;
constexpr int inf = 1000000010;
constexpr int inf2 = 2000000010;
constexpr ll INF = 1000000000000000010;
constexpr ll INF4 = 4000000000000000010;
constexpr int mod1e9 = 1000000007;
constexpr int mod998 = 998244353;
constexpr ld eps = 1e-12;
constexpr ld pi = 3.141592653589793238;
constexpr ll ten(int n) { return n ? 10 * ten(n - 1) : 1; };
int dx[] = { 1,0,-1,0,1,1,-1,-1,0 }; int dy[] = { 0,1,0,-1,1,-1,1,-1,0 };
ll mul(ll a, ll b) { return (b != 0 && a > INF / b ? INF : a * b); }
void fail() { cout << "-1\n"; exit(0); } void no() { cout << "No\n"; exit(0); }
template<class T> void er(T a) { cout << a << '\n'; exit(0); }
template<class T, class U> inline bool chmax(T& a, const U& b) { if (a < b) { a = b; return true; } return false; }
template<class T, class U> inline bool chmin(T& a, const U& b) { if (a > b) { a = b; return true; } return false; }
template<class T> istream& operator >>(istream& s, vector<T>& v) { for (auto& e : v) s >> e; return s; }
template<class T> ostream& operator <<(ostream& s, const vector<T>& v) { for (auto& e : v) s << e << ' '; return s; }
template<class T, class U> ostream& operator << (ostream& s, const pair<T, U>& p) { s << p.first << ' ' << p.second; return s; }

struct fastio {
	fastio() {
		cin.tie(0); cout.tie(0);
		ios::sync_with_stdio(false);
		cout << fixed << setprecision(20);
		cerr << fixed << setprecision(20);
	}
}fastio_;

namespace rdv {
	random_device seed_gen;
	mt19937_64 engine(seed_gen());
	ll rnum(ll r) { return engine() % r; } // [0, r)
	ll rnum(ll l, ll r) { return rnum(r - l) + l; } // [l, r)
	ll rng(ll l, ll r) { return rnum(l, r + 1); } // [l, r]
	double rng01() { return engine() * pow(2, -64); }
	template<class T> void shuf(vector<T>& v) { shuffle(all(v), engine); }
	void shuf(string& s) { shuffle(all(s), engine); }
}

using namespace rdv;

template<class T> vector<int> compress(vector<T> v) {
	int n = v.size();
	vector<T> tmp = v;
	sort(tmp.begin(), tmp.end());
	tmp.erase(unique(tmp.begin(), tmp.end()), tmp.end());
	vector<int> res(n);
	for (int i = 0; i < n; i++) res[i] = lower_bound(tmp.begin(), tmp.end(), v[i]) - tmp.begin();
	return res;
}

#include <atcoder/all>
using namespace atcoder;

constexpr ll mod = mod998;
using mint = static_modint<mod>;

istream& operator >>(istream& s, mint& m) { ll y; s >> y; m = y; return s; }
ostream& operator <<(ostream& s, mint& m) { return s << m.val(); }
ostream& operator <<(ostream& s, const vector<mint>& v) { for (auto& e : v) s << e.val() << ' '; return s; }

vector<mint> fac, inv, facinv;

void modcalc(int n) {
	fac.resize(n); inv.resize(n); facinv.resize(n);
	fac[0] = 1; fac[1] = 1; inv[1] = 1;
	facinv[0] = 1; facinv[1] = 1;
	for (ll i = 2; i < n; i++) {
		fac[i] = fac[i - 1] * i;
		inv[i] = -inv[mod % i] * (mod / i);
		facinv[i] = facinv[i - 1] * inv[i];
	}
}

mint comb(ll n, ll k) {
	if (n < 0 || k < 0 || n < k) return 0;
	return fac[n] * facinv[k] * facinv[n - k];
}

mint perm(ll n, ll k) {
	if (n < 0 || k < 0 || n < k) return 0;
	return fac[n] * facinv[n - k];
}

mint hom(ll n, ll k) {
	if (n < 0 || k < 0 || n == 0 && k > 0) return 0;
	if (n == 0 && k == 0) return 1;
	return fac[n + k - 1] * facinv[k] * facinv[n - 1];
}

vector<int> pf; // 最小素因数, pf[0] = pf[1] = 0
vector<int> prime; // 素数列

void sieve(int A) {
	pf.resize(A);
	for (int i = 2; i < A; i++) {
		if (pf[i] != 0) continue;
		prime.push_back(i);
		for (int j = i; j < A; j += i) if (pf[j] == 0) pf[j] = i;
	}
}

int op(int a, int b) { return a + b; }
int e() { return 0; }

int main() {
	int n;
	cin >> n;
	vector<ll> x(n), y(n);
	rep(i, n) cin >> x[i] >> y[i];
	mint ans = 0;
	mint inv2 = mint(1) / mint(2);
	for (int i = 1; i < n - 1; i++) {
		ll x0 = x[i] - x[0], y0 = y[i] - y[0];
		ll x1 = x[i + 1] - x[0], y1 = y[i + 1] - y[0];
		ll d = abs(x0 * y1 - x1 * y0);
		ans += mint(d) * inv2;
	}
	cout << ans << '\n';
}