#include <iostream>
#include <vector>
#include <utility>
#include <cstdio>
using namespace std;

#define X first
#define Y second

typedef pair<double,double> Pdd;

int main() {
  int n;
  double x, y;
  int cnt = 0;
  double ans;
  vector<Pdd> v;
  
  while(cin>>n, n) {
    v.clear();
    for(int i=0; i<n; i++) { cin>>x>>y; v.push_back(make_pair(x,y)); }
    
    ans = 0;
    for(int i=0; i<n; i++) {
      ans+=(v[(i+1)%n].X-v[i].X)*(v[(i+1)%n].Y+v[i].Y)/2;
    }
    
    printf("%d %.1f\n", ++cnt, ans);
  }
  
  return 0;
}