#include<iostream>
#include<algorithm>
#include <vector>
#include<cmath>
#include<cstdio>

using namespace std;
vector<pair<double, double> > v(51);
int main(void){
    int n;
    for(int __i = 1;cin >> n, n; __i++){
        for(int i = 0; i < n; i++){
            double a, b;
            cin >> a >> b;
            v[i] = make_pair(a, b);
        }
        v[n] = v[0];
        double area = 0;
        for(int i = 0;i < n; i++){
            area += v[i].first * v[i + 1].second - v[i + 1].first * v[i].second;
        }
        area = fabs(area)/2;
        printf("%d %.1f\n", __i, area);
    }
    return 0;
}