#include<cstdio>
#include<iostream>
#include<cstring>
#include<string.h>
#include<algorithm>
using namespace std;
const int maxn = 5000 + 5;
struct node
{
    int x1, x2, y1, y2;
    int id;
}k[maxn];
int x[maxn];
int y[maxn];
bool cmp1(node p, node q)
{
    if(p.x2==q.x2) return p.x1 < q.x1;
    return p.x2 < q.x2;
}
bool cmp2(node p, node q)
{
    if(p.y2==q.y2) return p.y1 < q.y1;
    return p.y2 < q.y2;
}
int main()
{
    int n;
    while(scanf("%d", &n) ==1 && n)
    {
        memset(k,0,sizeof(k));
        memset(x,0,sizeof(x));
        memset(y,0,sizeof(y));
        for(int i = 0; i < n; ++i)
            { scanf("%d%d%d%d", &k[i].x1, &k[i].y1, &k[i].x2, &k[i].y2); k[i].id = i;}
        int cnt[maxn];
        bool ok = false;
        memset(cnt,0,sizeof(cnt));
        sort(k,k+n, cmp1);
        for(int i = 0; i < n;++i)
        {
            ok = false;
            for(int j = k[i].x1; j <= k[i].x2; ++j)
            {
                if(!cnt[j])
                {
                    ok = true;
                    x[k[i].id] = j;
                    cnt[j] = 1;
                    break;
                }
            }
            if(!ok) break;
        }
        if(!ok)
        {
            cout << "IMPOSSIBLE" << endl;
            continue;
        }
        memset(cnt,0,sizeof(cnt));
        sort(k,k+n, cmp2);
        for(int i = 0; i < n;++i)
        {
            ok = false;
            for(int j = k[i].y1; j <= k[i].y2; ++j)
            {
                if(!cnt[j])
                {
                    ok = true;
                    y[k[i].id] = j;
                    cnt[j] = 1;
                    break;
                }
            }
            if(!ok) break;
        }
        if(!ok)
        {
            cout << "IMPOSSIBLE" << endl;
            continue;
        }
        for(int i = 0; i < n; ++i)
            printf("%d %d\n", x[i], y[i]);
    }
    return 0;
}