#include<bits/stdc++.h>

#define inf 0x3f3f3f3f

const int maxn=;

using namespace std;

int n;

struct rook{

        int x1,y1;

        int x2,y2;

        int id;

        int resx,resy;

        int size(){

                return abs(x1 - x2) * abs(x1 - x2) + abs(y1 - y2) * abs(y1 - y2);

        }

        int width(){

                return abs(x1 - x2);

        }

        int len(){

                return abs(y1 - y2);

        }

}rooks[maxn+];

int flagx[maxn+];

int flagy[maxn+];

bool cmpx(rook a, rook b){

        /*if(a.width() == b.width()){

              return a.x1 < b.x1;

        }

        return a.width() < b.width();*/

        //刚开始想错了，这么去贪心，是错的。

                                       /* 反例

                                        * 1111

                                        * 1

                                        *  1

                                        *   1

                                        *    11

                                        */

        if(a.x2 == b.x2){

                return a.x1 < b.x1;

        }

        return a.x2 < b.x2;

}

bool cmpy(rook a, rook b){

        /*if(a.len() == b.len()){

              return a.y1 < b.y1;

        }

        return a.len() < b.len();*/

        if(a.y2 == b.y2){

                return a.y1 < b.y1;

        }

        return a.y2 < b.y2;

}

bool cmp1(rook a, rook b){

        return a.id < b.id;

}

int main()

{

        while(scanf("%d",&n)!=EOF&&n){

                int res = ;

                memset(flagx, , sizeof(flagx));

                memset(flagy, , sizeof(flagy));

                for(int i = ; i < n; ++i){

                        scanf("%d%d%d%d",&rooks[i].x1,&rooks[i].y1,&rooks[i].x2,&rooks[i].y2);

                        rooks[i].id = i;

                }

                sort(rooks, rooks + n, cmpx);

                for(int i = ; i < n; ++i){

                        int flag = ;

                        for(int j = rooks[i].x1; j <= rooks[i].x2; ++j){

                                if(!flagx[j]){

                                        flagx[j] = ;

                                        rooks[i].resx = j;

                                        flag = ;

                                        break;

                                }

                        }

                        if(!flag){

                                res = ;

                                break;

                        }

                }

                if(!res){

                        sort(rooks, rooks + n, cmpy);

                        for(int i = ; i < n; ++i){

                                int flag = ;

                                for(int j = rooks[i].y1; j <= rooks[i].y2; ++j){

                                        if(!flagy[j]){

                                                flagy[j] = ;

                                                rooks[i].resy = j;

                                                flag = ;

                                                break;

                                        }

                                }

                                if(!flag){

                                        res = ;

                                        break;

                                }

                        }

                }

                if(res){

                        printf("IMPOSSIBLE\n");

                } else {

                        sort(rooks, rooks + n, cmp1);

                        for(int i = ; i < n; ++i){

                                printf("%d %d\n",rooks[i].resx,rooks[i].resy);

                        }

                }

        }

    return ;

}