#include<bits/stdc++.h>
using namespace std;
#define N 5010
int n,k;
int vis[N];
struct node
{int id;int x,y;int x1,x2,y1,y2;}chess[N];bool cmp1(node a,node b){return a.x2<b.x2||(a.x2==b.x2&&a.x1<b.x1);}
bool cmp2(node a,node b){return a.y2<b.y2||(a.y2==b.y2&&a.y1<b.y1);}
bool cmp3(node a,node b){return a.id<b.id;}
int main()
{while(cin>>n,n){int flag=1;for(int i=0;i<n;i++){chess[i].id=i;scanf("%d%d%d%d",&chess[i].x1,&chess[i].y1,&chess[i].x2,&chess[i].y2);}sort(chess,chess+n,cmp1);memset(vis,0,sizeof vis);for(int i=0;i<n;i++){int ok=0;for(int j=chess[i].x1;j<=chess[i].x2;j++){if(!vis[j]){ok=1;vis[j]=1;chess[i].x=j;break; }//把chess里面的i写成了j  强行将自己dubug了半个小时。。。
            }if(!ok){flag=0;}}sort(chess,chess+n,cmp2);memset(vis,0,sizeof vis);for(int i=0;i<n;i++){int ok=0;for(int j=chess[i].y1;j<=chess[i].y2;j++){if(!vis[j]){ok=1;vis[j]=1;chess[i].y=j;break; }}if(!ok){flag=0;}}sort(chess,chess+n,cmp3);if(flag)for(int i=0;i<n;i++)printf("%d %d\n",chess[i].x,chess[i].y);else printf("IMPOSSIBLE\n");}
}

#include<cstdio>
#include<cstring>
#include <algorithm>
using namespace std;// solve 1-D problem: find c so that a[i] <= c[i] <= b[i] (0 <= i < n)
bool solve(int *a, int *b, int *c, int n) {fill(c, c+n, -1);for(int col = 1; col <= n; col++) {// find a rook with smalleset b that is not yet assignedint rook = -1, minb = n+1;for(int i = 0; i < n; i++)if(c[i] < 0 && b[i] < minb && col >= a[i]) { rook = i; minb = b[i]; }if(rook < 0 || col > minb) return false;c[rook] = col;}return true;
}const int maxn = 5000 + 5;
int n, x1[maxn], y1[maxn], x2[maxn], y2[maxn], x[maxn], y[maxn];int main() {while(scanf("%d", &n) == 1 && n) {for (int i = 0; i < n; i++)scanf("%d%d%d%d", &x1[i], &y1[i], &x2[i], &y2[i]);if(solve(x1, x2, x, n) && solve(y1, y2, y, n))for (int i = 0; i < n; i++) printf("%d %d\n", x[i], y[i]);elseprintf("IMPOSSIBLE\n");}return 0;
}