#include <stdio.h>double det(double x1,double y1,double x2,double y2,double x3,double y3){ return x1*y2+x2*y3+x3*y1-x2*y1-x3*y2-x1*y3;}int main(){ int n,i,j,count=0,temp; double x[1000],y[1000],area; while(1) { scanf("%d",&n); if (n==0) return 0; count++; if (count>1) printf("n"); printf("Figure %d: ",count); for(i=0;i<n;i++) scanf("%lf%lf",&x[i],&y[i]); if (n<3){ printf("Impossiblen"); continue; } for(i=0;i<n;i++) for(j=(i+1)/n;j<i-1;j++){ temp=(i+1)%n; if (det(x[j],y[j],x[i],y[i],x[j+1],y[j+1])*det(x[j],y[j],x[temp],y[temp],x[j+1],y[j+1])<=0&& det(x[i],y[i],x[j],y[j],x[temp],y[temp])*det(x[i],y[i],x[j+1],y[j+1],x[temp],y[temp])<=0) { printf("Impossiblen"); goto quit; } } area=0; for(i=0;i<n;i++){ area+=x[i]*y[(i+1)%n]; area-=y[i]*x[(i+1)%n]; } if (area<0) area*=-1; printf("%.2lfn",area/2);quit:; }}
