#include <stdio.h>#include <algorithm>#include <cstring>#include <cmath>using namespace std;const int N = 2010;const double eps = 1e-6;const double PI = acos(-1);struct point{    double x, y;    int Id;    point(){}    point(double x, double y) : x(x), y(y) {}    point friend operator - (const point &p1, const point &p2)///矢量p2p1;    {        return point(p1.x-p2.x, p1.y-p2.y);    }    double friend operator ^ (const point &p1, const point &p2)///p1×p2;    {        return p1.x*p2.y - p1.y*p2.x;    }};point p[N];double Dist(point p1, point p2){    double dx = p1.x - p2.x, dy = p1.y - p2.y;    return sqrt(dx*dx + dy*dy);}int cmp1(point p1, point p2)///位置排序，找到最下方的；{    if(p1.y != p2.y)        return p1.y < p2.y;    return p1.x < p2.x;///若有多个下方的找左边的；}int cmp2(point p1, point p2)///极角排序；若极角相同，距离近的在前面；{    double k = (p1-p[0])^(p2-p[0]);    if( k>eps || (fabs(k)<eps && Dist(p1, p[0]) < Dist(p2, p[0]) ))        return 1;    return 0;}int main(){    int n, T, t=1;    scanf("%d", &T);    while(T--)    {        scanf("%d", &n);        for(int i=0; i<n; i++)        {            scanf("%lf %lf", &p[i].x, &p[i].y);            p[i].Id = i;        }        sort(p, p+n, cmp1);///p[0]为最下方靠左的点；        sort(p+1, p+n, cmp2);///以p[0]为基点，按叉积进行排序；        int flag = 0;        for(int i=n-2; i>0; i--)        {            if(((p[n-1]-p[0])^(p[i]-p[0]))!=0)            {                flag = i;                break;            }        }        printf("Case %d:\n", t++);        if(flag==0)        {            printf("Impossible\n");            continue;        }        reverse(p+flag+1, p+n);        for(int i=0; i<n; i++)            printf("%d%c", p[i].Id, i==n-1?‘\n‘:‘ ‘);    }    return 0;}