#include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <ctime>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <set>
#include <map>
#include <iostream>
#include <deque>
#include <complex>
#include <string>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <valarray>
#include <iterator>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) container.begin(), container.end()
#define RALL(container) container.rbegin(), container.rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;

namespace geom{
#define X real()
#define Y imag()
	
	typedef double R;
	typedef complex<R> P;
	struct L : public vector<P>{
		L(const P &p1, const P &p2){this->push_back(p1);this->push_back(p2);}
	};
	istream& operator>>(istream &is, P &p) {
		double x, y;
		is >> x >> y;
		p = P(x, y);
		return is;
	}
	inline int sig(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
	inline R norm(const P &p){return p.X*p.X+p.Y*p.Y;}
	inline R inp(const P& a, const P& b){return (conj(a)*b).X;}
	inline R outp(const P& a, const P& b){return (conj(a)*b).Y;}
	inline P unit(const P& p){return p/abs(p);}
	inline P proj(const P &s, const P &t){return t*inp(s, t)/norm(t);}
	inline P proj(const P &s, const L &t){return t[0] + proj(s-t[0], t[1]-t[0]);}
	inline bool sp_intersect(const L &s, const P &p){return !sig(abs(s[0]-p) + abs(s[1] - p) - abs(s[0] - s[1]));}
	
	struct G : public vector<P>{
		enum {OUT, IN, ON};
		P &at(int i){return (*this)[i];}
		bool contains(const P &p){
			R sum = .0;
			REP(i, size()){
				if(sp_intersect(L(at(i), at((i+1)%size())), p)) return ON;	// online
				sum += arg((at(i) - p) / (at((i+1)%size()) - p));
			}
			return sig(sum) ? IN : OUT;
		}
		
		R area(){
			R sum = 0;
			REP(i, size()) sum += outp(at(i), at((i+1)%size()));
			return abs(sum / 2.);
		}
	};
};
using namespace geom;

int n;

int main(){
	ios::sync_with_stdio(false);
	int T = 0;
	for(int T = 1;cin >> n, n;T++){
		P p;
		G g;
		REP(i, n){
			cin >> p;
			g.push_back(p);
		}
		printf("%d %.1f\n", T, g.area());
	}
	return 0;
}

Measured memory_bytes: 1272