#ifndef _DEBUG
#define _DEBUG
#include __FILE__

signed main() {
  int N;
  cin >> N;
  vector<point> P(N);
  for (int i = 0; i < N; i++) {
    int x, y;
    cin >> x >> y;
    P.at(i) = {x, y};
  }

  reverse(P.begin(), P.end());

  polygon poly;
  for (const auto& a : P) bg::append(poly, a);
  bg::append(poly, P.front());
  cout << long(mp::round(bg::area(poly) * 2)) << "\n";
}

#else
// #undef _DEBUG
#pragma GCC diagnostic warning "-Wextra"
#pragma GCC diagnostic warning "-Wshadow"
#include <bits/stdc++.h>
using namespace std;

#include <boost/geometry.hpp>
#include <boost/multiprecision/cpp_dec_float.hpp>

namespace bg = boost::geometry;
namespace mp = boost::multiprecision;

// typedef bg::model::d2::point_xy<mp::cpp_dec_float_50> point;
typedef bg::model::point<mp::cpp_dec_float_50, 2, bg::cs::cartesian> point;
typedef bg::model::segment<point> segment;
typedef bg::model::linestring<point> line;
typedef bg::model::ring<point> ring;
typedef bg::model::box<point> box;
typedef bg::model::polygon<point> polygon;

struct io_setup {
  io_setup() { cin.tie(nullptr)->sync_with_stdio(false); }
} io_setup;

template <class A, class B> bool cmin(A& a, const B& b) {
  if (a > b) return a = b, true;
  return false;
}

template <class A, class B> bool cmax(A& a, const B& b) {
  if (a < b) return a = b, true;
  return false;
}

template <class A, class B> ostream& operator<<(ostream& os, const pair<A, B>& p);

template <class A, class B, class C> ostream& operator<<(ostream& os, const tuple<A, B, C>& t);

template <class A, class B, class C, class D> ostream& operator<<(ostream& os, const tuple<A, B, C, D>& t);

#define foreach(it, a) for (auto it = a.begin(); it != a.end(); it++)

ostream& operator<<(ostream& os, const vector<char>& vec) {
  os << "{";
  foreach (it, vec) { os << (it == vec.begin() ? "" : " ") << *it; }
  return os << "}";
}

template <class A> ostream& operator<<(ostream& os, const vector<A>& vec) {
  os << "{";
  foreach (it, vec) { os << (it == vec.begin() ? "" : ", ") << *it; }
  return os << "}";
}

template <class A> ostream& operator<<(ostream& os, const vector<vector<A> >& vec) {
  os << "{\n";
  foreach (it, vec) { os << (it == vec.begin() ? " " : "\n ") << *it; }
  return os << "\n}";
}

template <class A> ostream& operator<<(ostream& os, const vector<vector<vector<A> > >& vec) {
  os << "{\n";
  foreach (it, vec) { os << (it == vec.begin() ? "" : "\n") << it - vec.begin() << ": " << *it; }
  return os << "\n}";
}

template <class A> ostream& operator<<(ostream& os, const set<A>& se) {
  os << "{";
  foreach (it, se) { os << (it == se.begin() ? "" : ", ") << *it; }
  return os << "}";
}

template <class A> ostream& operator<<(ostream& os, const multiset<A>& ms) {
  os << "{";
  foreach (it, ms) { os << (it == ms.begin() ? "" : ", ") << *it; }
  return os << "}";
}

template <class A, class B> ostream& operator<<(ostream& os, const map<A, B>& ma) {
  os << "{";
  foreach (it, ma) { os << (it == ma.begin() ? "" : ", ") << *it; }
  return os << "}";
}

template <class A> ostream& operator<<(ostream& os, priority_queue<A> pq) {
  os << "{";
  while (!pq.empty()) {
    os << pq.top(), pq.pop();
    if (!pq.empty()) os << ", ";
  }
  return os << "}";
}

template <class A, class B> ostream& operator<<(ostream& os, const pair<A, B>& p) {
  const auto& [a, b] = p;
  return os << "(" << a << ", " << b << ")";
}

template <class A, class B, class C> ostream& operator<<(ostream& os, const tuple<A, B, C>& t) {
  const auto& [a, b, c] = t;
  return os << "(" << a << ", " << b << ", " << c << ")";
}

template <class A, class B, class C, class D> ostream& operator<<(ostream& os, const tuple<A, B, C, D>& t) {
  const auto& [a, b, c, d] = t;
  return os << "(" << a << ", " << b << ", " << c << ", " << d << ")";
}

void dump_func() {}
template <class A, class... B> void dump_func(const A& a, const B&... b) {
  cout << a << (sizeof...(b) ? ", " : "\n");
  dump_func(b...);
}

#ifdef _DEBUG
#define dump(...) cout << "[" << (#__VA_ARGS__) << "]: ", dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif
#endif