sicily 1741

#include "iostream"
#include "iomanip"
using namespace std;

struct Info
{
    int X;
    int Y;
};

double area(double a, double b, double c, double d)
{
    double differX = c - a;
    double differY;
    double mult1 = 0, mult2 = 0;
    if (b > d)
    {
        mult1 = differX * d;
        differY = b - d;
    }
    else
    {
        mult1 = differX * b;
        differY = d - b;
    }
     mult2 = differX * differY / 2;
     return (mult1 + mult2);
}

int main()
{
    int T;
    cin >> T;
    while (T--)
    {
        int N;
        cin >> N;
        Info *a = new Info[N];
        for (int i = 0; i < N; i++)
            cin >> a[i].X >> a[i].Y;
        double areaSum = 0;
        for (int i = 0; i < N-1; i++)
            areaSum += area(a[i].X, a[i].Y, a[i+1].X, a[i+1].Y);
       /* cout.setf(ios_base::showbase);
        cout.setf(ios_base::fixed);
        cout.setf(ios_base::floatfield);
        cout.setf(ios_base::showpoint);
        cout.precision(2);
        cout << setiosflags(ios::showpoint) << areaSum << endl;*/
        cout << fixed << setprecision(1) << areaSum << endl;
    }
}