#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;

int main()
{
    int num;
    int count = 1;

    while (true) {
        cin >> num;
        if (num == 0) 
            break;

        double area = 0.0;
        int x1, y1, bx, by, ax, ay;
        cin >> x1 >> y1;
        bx = x1;
        by = y1;

        for (int i = 1; i < num; i++) {
            cin >> ax >> ay;
            area += bx * ay - ax * by;
            bx = ax;
            by = ay;
        }
        area += bx * y1 - x1 * by;

        cout << setprecision(1) << fixed;
        cout << count++ << " " << 0.5 * abs(area) << endl;
    }

    return 0;
}