#include <cstdio>
#include <vector>
#include <algorithm>
#include <map>
#include <set>
#include <cmath>
#include <iostream>
#include <ctime>
#include <utility>
#include <string>
#include <memory.h>
using namespace std;

#define forn( i,n ) for ( int i=0; i<(int)(n); i++ )
#define sz(a) (int)((a).size())
#define pb push_back
#define mp make_pair
typedef long long ll;
typedef double ld;
typedef pair<int,int> pii;

const int maxn = 100005;
const ld pi = acos(-1.0);
const ld eps = 1e-8;
const ld ang = 0.732423543;
const ld co = cos(ang);
const ld si = sin(ang);

struct point
{
  ld x, y;
  int id;
};


bool operator<(const point& a, const point& b)
{
  if (fabs(a.x-b.x) > eps) return a.x < b.x;
  if (fabs(a.y-b.y) > eps) return a.y < b.y;
  return a.id < b.id;
}

ld dist(const point& a, const point& b)
{
  return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
}


point a[maxn];
int b[maxn];
vector<int> ans[maxn];
int n;

int main()
{
  freopen( "a.in", "r", stdin );
  freopen( "a.out", "w", stdout );


  scanf("%d", &n);
  forn (i, n)
  {
    int x, y; scanf("%d %d", &x, &y);
    a[i].x = co*x + si*y;
    a[i].y = -si*x + co*y;
  }

  sort(a, a+n);
  forn (i, n)
  {
    ld d = 1e15;
    int q = -1;

    for (int j=i-1; j>=0; --j)
    {
      if (a[i].x > a[j].x + d) break;
      ld dd = dist(a[i], a[j]);
      if (d > dd) d = dd, q = a[j].id;
    }
    for (int j=i+1; j<n; ++j)
    {
      if (a[j].x > a[i].x + d) break;
      ld dd = dist(a[i], a[j]);
      if (d > dd) d = dd, q = a[j].id;
    }

    b[i] = q;
  }
  forn (i, n) ans[b[i]].pb(i);
  forn (i, n)
  {
    printf("%d:", i+1);
    forn (j, sz(ans[i])) printf(" %d", ans[i][j]+1);
    puts("");
  }




  return 0;
}










































































#include <cstdio>
#include <vector>
#include <algorithm>
#include <map>
#include <set>
#include <cmath>
#include <iostream>
#include <ctime>
#include <utility>
#include <string>
#include <memory.h>
using namespace std;

#define forn( i,n ) for ( int i=0; i<(int)(n); i++ )
#define sz(a) (int)((a).size())
#define pb push_back
#define mp make_pair
typedef long long ll;
typedef double ld;
typedef pair<int,int> pii;

const int maxn = 100005;
const ld pi = acos(-1.0);
const ld eps = 1e-8;
const ld ang = 0.732423543;
const ld co = cos(ang);
const ld si = sin(ang);

struct point
{
  ld x, y;
  int id;
};


bool operator<(const point& a, const point& b)
{
  if (fabs(a.x-b.x) > eps) return a.x < b.x;
  if (fabs(a.y-b.y) > eps) return a.y < b.y;
  return a.id < b.id;
}

ld dist(const point& a, const point& b)
{
  return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
}


point a[maxn];
int b[maxn];
vector<int> ans[maxn];
int n;

int main()
{
  freopen( "a.in", "r", stdin );
  freopen( "a.out", "w", stdout );


  scanf("%d", &n);
  forn (i, n)
  {
    int x, y; scanf("%d %d", &x, &y);
    a[i].x = co*x + si*y;
    a[i].y = -si*x + co*y;
  }

  sort(a, a+n);
  forn (i, n)
  {
    ld d = 1e15;
    int q = -1;

    for (int j=i-1; j>=0; --j)
    {
      if (a[i].x > a[j].x + d) break;
      ld dd = dist(a[i], a[j]);
      if (d > dd) d = dd, q = a[j].id;
    }
    for (int j=i+1; j<n; ++j)
    {
      if (a[j].x > a[i].x + d) break;
      ld dd = dist(a[i], a[j]);
      if (d > dd) d = dd, q = a[j].id;
    }

    b[i] = q;
  }
  forn (i, n) ans[b[i]].pb(i);
  forn (i, n)
  {
    printf("%d:", i+1);
    forn (j, sz(ans[i])) printf(" %d", ans[i][j]+1);
    puts("");
  }




  return 0;
}