import std.stdio;
import std.algorithm;
import std.string;
import std.range;
import std.array;
import std.conv;
import std.complex;
import std.math;
import std.ascii;
import std.bigint;
import std.container;

int cross(int[] r1, int[] r2) {
	return r1[0]*r2[1]-r1[1]*r2[0];
}

void main() {
	int n = to!int(readln().strip());
	int c;
	while(n) {
		int[] p0 = array(map!(to!int)(readln().strip().split()));
		int[][] p;
		foreach(i; 1..n) {
			auto pi = map!(to!int)(readln().strip().split());
			p ~= [pi[0]-p0[0], pi[1]-p0[1]];
		}
		int s;
		foreach(i; 1..n-1) {
			s += cross(p[i], p[i-1]);
		}
		writefln("%d %.1f", ++c, abs(s/2.0));

		readln();
		n = to!int(readln().strip());
	}
}