#include<deque>
#include<list>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<vector>
#include<algorithm>
#include<string>
#include<iostream>
#include<sstream>
#include<cmath>
#include<cstdio>
#include<cstring>
using namespace std;
int main(){
  int h,i;
  int n;
  for(h=1;cin>>n,n;h++){
    int x[50],y[50];
    for(i=0;i<n;i++)
      cin>>x[i]>>y[i];
    int sm=0;
    for(i=2;i<n;i++)
      sm+=(x[i-1]-x[0])*(y[i]-y[0])-(x[i]-x[0])*(y[i-1]-y[0]);
    printf("%d %.1lf\n",h,fabs(sm)/2);
  }
  return 0;
}