#include<bits/stdc++.h>
using namespace std;

//objects-----------------------------------------------------------------
typedef complex<double>Point;
typedef Point Vector;
typedef vector<Point>Polygon;

struct Segment{
    Point p1,p2;
    Segment(const Point &p1=Point(),const Point &p2=Point()):p1(p1),p2(p2){}
};

struct Line{
    Point p1,p2;
    Line(const Point &p1=Point(),const Point &p2=Point()):p1(p1),p2(p2){}
};

struct Circle{
    Point p;
    double r;
    Circle(const Point &p=Point(),double r=0.0):p(p),r(r){}
};

//constants---------------------------------------------------------------
const double PI=acos(-1);
const double EPS=1e-12;
const double INF=1e16;
const int COUNTER_CLOCKWISE=1;
const int CLOCKWISE=-1;
const int ONLINE_BACK=2;
const int ONLINE_FRONT=-2;
const int ON_SEGMENT=0;
const int IN=2;
const int ON=1;
const int OUT=0;
//calculations------------------------------------------------------------
inline double square(double a){return a*a;}
inline double norm(const Point &a){return square(a.real())+square(a.imag());}
inline double dot(const Point &a,const Point &b){return (conj(a)*b).real();}
inline double cross(const Point &a,const Point &b){return (conj(a)*b).imag();}
inline double toDeg(double t){return t/PI*180.0;}
inline double toRad(double t){return t/180.0*t;}
inline double arg(Vector p){return atan2(imag(p),real(p));}
inline Vector polar(double a,double r){return Vector(cos(r),sin(r))*a;}
#define equals(a,b) (fabs((a)-(b))<EPS)
#define equalsv(a,b) (equals(real(a),real(b))&&equals(imag(a),imag(b)))
#define curr(P,i) P[(i)%P.size()]
#define next(P,i) P[(i+1)%P.size()]
#define prev(P,i) P[(i-1+P.size())%P.size()]

int ccw(Point p0,Point p1,Point p2){
    Vector a=p1-p0;
    Vector b=p2-p0;
    if(cross(a,b)>EPS)return COUNTER_CLOCKWISE;
    if(cross(a,b)<-EPS)return CLOCKWISE;
    if(dot(a,b)<EPS)return ONLINE_BACK;
    if(norm(a)<norm(b))return ONLINE_FRONT;
    return ON_SEGMENT;
}

//inputer-----------------------------------------------------------------
void inputPoint(Point &p){
    double x,y;
    scanf("%lf%lf",&x,&y);
    p=Point(x,y);
}

void inputSegment(Segment &s){
    inputPoint(s.p1);
    inputPoint(s.p2);
}

void inputLine(Line &l){
    inputPoint(l.p1);
    inputPoint(l.p2);
}

void inputCircle(Circle &c){
    inputPoint(c.p);
    scanf("%lf",&c.r);
}

void inputPolygon(Polygon &g,int n){
    g.resize(n);
    for(int i=0;i<n;i++)inputPoint(g[i]);
}

//orthogonal--------------------------------------------------------------
bool orthogonal(Vector a,Vector b){
    return equals(dot(a,b),0.0);
}

bool orthogonal(Point a1,Point a2,Point b1,Point b2){
    return orthogonal(a1-a2,b1-b2);
}

bool orthogonal(Segment s1,Segment s2){
    return orthogonal(s1.p1-s1.p2,s2.p1-s2.p2);
}

bool orthogonal(Line l1,Line l2){
    return orthogonal(l1.p1-l1.p2,l2.p1-l2.p2);
}

//parallel----------------------------------------------------------------
bool parallel(Vector a,Vector b){
    return equals(cross(a,b),0.0);
}

bool parallel(Point a1,Point a2,Point b1,Point b2){
    return parallel(a1-a2,b1-b2);
}

bool parallel(Segment s1,Segment s2){
    return parallel(s1.p1-s1.p2,s2.p1-s2.p2);
}

bool parallel(Line l1,Line l2){
    return parallel(l1.p1-l1.p2,l2.p1-l2.p2);
}

//project&reflect---------------------------------------------------------
Point project(Line s,Point p){
    Vector base=s.p2-s.p1;
    double r=dot(p-s.p1,base)/norm(base);
    return s.p1+base*r;
}

Point reflect(Line s,Point p){
    return p+(project(s,p)-p)*2.0;
}

//distance----------------------------------------------------------------
double distancePP(Point a,Point b){
    return abs(a-b);
}

double distanceLP(Line l,Point p){
    return fabs(cross(l.p2-l.p1,p-l.p1)/abs(l.p2-l.p1));
}

double distanceLL(Line l,Line m){
    if(parallel(l,m))return distanceLP(l,m.p1);
    return 0.0;
}

double distanceSP(Segment s,Point p){
    if(dot(s.p2-s.p1,p-s.p1)<0.0)return distancePP(p,s.p1);
    if(dot(s.p1-s.p2,p-s.p2)<0.0)return distancePP(p,s.p2);
    return distanceLP(Line(s.p1,s.p2),p);
}

double distanceSS(Segment s1,Segment s2){
    if(ccw(s1.p1,s1.p2,s2.p1)*ccw(s1.p1,s1.p2,s2.p2)<=0&&
        ccw(s2.p1,s2.p2,s1.p1)*ccw(s2.p1,s2.p2,s1.p2)<=0)return 0;
    return min(min(distanceSP(s1,s2.p1),distanceSP(s1,s2.p2)),
            min(distanceSP(s2,s1.p1),distanceSP(s2,s1.p2)));
}

double distanceCS(Circle c,Segment s){
    return distanceSP(s,c.p)-c.r;
}

//intersect----------------------------------------------------------------
bool intersectSS(Point p1,Point p2,Point p3,Point p4){
    return ccw(p1,p2,p3)*ccw(p1,p2,p4)<=0&&
            ccw(p3,p4,p1)*ccw(p3,p4,p2)<=0;
}

bool intersectSS(Segment s1,Segment s2){
    return intersectSS(s1.p1,s1.p2,s2.p1,s2.p2);
}

bool intersectCL(Circle c,Line l){
    return fabs(cross(l.p2-l.p1,c.p-l.p1)/abs(l.p2-l.p1))<=c.r+EPS;
}

bool intersectCC(Circle c1,Circle c2){
    return abs(c1.p-c2.p)<=c1.r+c2.r+EPS;
}

bool intersectCS(Circle c,Segment s){
    return distanceSP(s,c.p)<=c.r+EPS;
}

bool intersectGC(Polygon g,Circle c){
    for(int i=0;i<g.size();i++){
        Segment s(g[i],next(g,i));
        if(intersectCS(c,s))return true;
    }
    return false;
}

//crossPoint--------------------------------------------------------------
Point crossPoint(Segment s1,Segment s2){
    double crs=cross(s1.p2-s1.p1,s2.p2-s2.p1);
    return s2.p1+(s2.p2-s2.p1)*cross(s1.p2-s1.p1,s1.p2-s2.p1)*(1.0/crs);
}

pair<Point,Point>crossPoints(Circle c,Line l){
    assert(intersectCL(c,l));
    Vector pr=project(l,c.p);
    Vector e=(l.p2-l.p1)/abs(l.p2-l.p1);
    double base=sqrt(square(c.r)-norm(pr-c.p));
    return make_pair(pr+e*base,pr-e*base);
}

pair<Point,Point>crossPoints(Circle c1,Circle c2){
    assert(intersectCC(c1,c2));
    double d=abs(c1.p-c2.p);
    double a=acos((square(c1.r)+square(d)-square(c2.r))/(2*c1.r*d));
    double t=arg(c2.p-c1.p);
    return make_pair(c1.p+polar(c1.r,t+a),c1.p+polar(c1.r,t-a));
}

//polygon------------------------------------------------------------------
double area(Polygon &g){
    const int sz=g.size();
    double res=cross(g[sz-1],g[0]);
    for(int i=1;i<sz;i++)res+=cross(g[i-1],g[i]);

    return fabs(res)*0.5;
}

bool convex(Polygon &g){
    for(int i=0;i<g.size();i++){
        if(ccw(prev(g,i),curr(g,i),next(g,i))==CLOCKWISE)return false;
    }
    return true;
}

//contains-------------------------------------------------------------------
int contains(Circle c,Point p){
    double d=distancePP(c.p,p);
    if(equals(d,c.r))return ON;
    return d<c.r?IN:OUT;
}

int contains(Polygon g,Point p){
    int n=g.size();
    bool x=false;
    for(int i=0;i<n;i++){
        Point a=g[i]-p,b=next(g,i)-p;
        if(abs(cross(a,b))<EPS&&dot(a,b)<EPS)return ON;
        if(imag(a)>imag(b))swap(a,b);
        if(imag(a)<EPS&&EPS<imag(b)&&cross(a,b)>EPS)x=!x;
    }
    return x?IN:OUT;
}

int contains(Circle c,Polygon g){
    for(int i=0;i<g.size();i++){
        if(!contains(c,g[i]))return OUT;
    }
    return IN;
}

int contains(Polygon g,Circle c){
    if(contains(g,c.p)!=IN)return OUT;
    for(int i=0;i<g.size();i++){
        if(distanceCS(c,Segment(g[i],next(g,i)))<-EPS)return OUT;
    }
    return IN;
}
//end---------------------------------------------------------------------



int main(){
    int n;
    int c=0;
    while(cin>>n,n){
        c++;
        Polygon g(n);
        for(int i=0;i<n;i++)inputPoint(g[i]);
        printf("%d %.1lf\n",c,area(g));
    }
    return 0;
}

Measured memory_bytes: 1284