#include <iostream>
#include <stdio.h>
#include <vector>
#include <cmath>

using namespace std;

class Point
{
public:
	int x, y;
};

void solve()
{
	int count = 1;
	int n;
	while(cin >> n, n)
	{
		vector<Point> p(n);
		for(int i = 0; i < n; ++i)
		{
			cin >> p[i].x >> p[i].y;
		}
		double sum = 0.0;
		for(int i = 1; i < n - 1; ++i)
		{
			double x1 = p[i].x - p[0].x;
			double y1 = p[i].y - p[0].y;
			double x2 = p[i + 1].x - p[0].x;
			double y2 = p[i + 1].y - p[0].y;
			sum += x1 * y2 - x2 * y1;
		}
		printf("%d %.1f\n", count, abs(sum) / 2);
		++count;
	}
}

int main()
{
	solve();
	return(0);
}