#include <iostream>

 #include <algorithm>

 #include <cstring>

 using namespace std;

 const int maxn =  + ;

 struct point{

     int st, ed, id;

 }x[maxn], y[maxn];

 int n, cx[maxn], cy[maxn];

 bool cmp(const point& temp1, const point& temp2) {

     return temp1.ed == temp2.ed ? temp1.st < temp2.st : temp1.ed < temp2.ed;

 }

 bool judge(int *arr, point *Point) {

     sort(Point, Point + n, cmp);

     int temp[maxn] = {};

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

         bool ok = false;

         for(int j = Point[i].st; j <= Point[i].ed; j++) {

             if(!temp[j]) {

                 ok = true;

                 temp[j] = ;

                 arr[Point[i].id] = j;

                 break;

             }

         }

         if(!ok) return false;

     }

     return true;

 }

 int main()

 {

     while(cin >> n && n) {

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

             cin >> x[i].st >> y[i].st >> x[i].ed >> y[i].ed;

             x[i].id = i;

             y[i].id = i;

         }

         memset(cx, , sizeof(cx));

         memset(cy, , sizeof(cy));

         if(judge(cx, x) && judge(cy, y)) {

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

                 cout << cx[i] << ' ' << cy[i] << endl;

         }

         else

             cout << "IMPOSSIBLE" << endl;

     }

     return ;

 }