#include <cstdio>
#include <complex>
#include <cmath>
#include <vector>

using namespace std;

typedef complex<double> xy_t;

double cross_product(xy_t a, xy_t b) {
	return (conj(a) * b).imag();
}

int main() {
	int id = 1;
	while (1) {
		int n;
		double x, y;
		double s = 0;
		scanf("%d", &n);
		if (n == 0) return 0;
		vector<xy_t> vertex;
		for (int i = 0; i < n; i++) {
			scanf("%lf %lf", &x, &y);
			vertex.push_back(xy_t(x, y));
		}
		for (int i = 1; i < vertex.size() - 1; i++) {
			s += cross_product(vertex[i + 1] - vertex[0], vertex[i] - vertex[0]) / 2;
		}
		printf("%d %.1f\n", id, s);
		id++;
	}
}