#include <fstream>
#include <cmath>
#include <algorithm>
#define N 1000002
#include <iomanip>

using namespace std;
ifstream f("aria.in");
ofstream g("aria.out");

long double xG, yG;
struct bla
{
    long double x, y;
}v[N];
bool cmp(bla A, bla B)
{
    return (atan2(A.x - xG, A.y - yG) < atan2(B.x - xG, B.y - yG));
}
long double det(long double x1, long double y1, long double x2, long double y2)
{
    return (x1 * y2 - x2 * y1);
}
int main()
{
    int n;
    f >> n;
    for (int i = 1;i <= n;++i)
        f >> v[i].x >> v[i].y, xG = xG + v[i].x, yG = yG + v[i].y;
    xG = xG / n;
    yG = yG / n;
    sort(v + 1, v + n + 1, cmp);
    long double arie = 0;
    v[n + 1] = v[1];
    ++n;
    for (int i = 2;i <= n;++i)
        arie = arie + det(v[i - 1].x, v[i - 1].y, v[i].x, v[i].y);
    arie = arie * 0.5;
    g << fixed << setprecision(5) << -arie;
    f.close();
    g.close();
    return 0;
}