uva 11143

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #define maxn 5100
 #include<queue>
 using namespace std;

 struct node
 {
     int x,y;
     int id;
     bool operator<(const node &t)const
     {
         return y>t.y;
     }
 } hang[maxn],lie[maxn];

 bool cmp(const node &a,const node &b)
 {
     return a.x<b.x;
 }

 int h[maxn],l[maxn];

 priority_queue<node>q;

 int main()
 {
     int n;
     while(scanf("%d",&n)&&n)
     {
         for(int i=; i<n; i++)
         {
             scanf("%d%d%d%d",&hang[i].x,&lie[i].x,&hang[i].y,&lie[i].y);
             hang[i].id=lie[i].id=i;
             h[i]=;
             l[i]=;
         }
         sort(hang,hang+n,cmp);
         int cur=;
         int timer=;
         bool flag=;
         while(!q.empty())q.pop();
         while()
         {
             while(cur<n&&hang[cur].x<=timer)q.push(hang[cur++]);
             if(timer<=n&&q.empty())
                 {
                     flag=;
                     break;
                 }
             node v=q.top();
             q.pop();
             if(timer<v.x||timer>v.y)
             {
                 flag=;
                 break;
             }
             h[v.id]=timer;
             timer++;
             if(timer>n)break;
         }
         if(flag)
         {
             sort(lie,lie+n,cmp);
             cur=;
             timer=;
             while(!q.empty())q.pop();
             while()
             {
                 while(cur<n&&lie[cur].x<=timer)q.push(lie[cur++]);
                 if(timer<=n&&q.empty())
                 {
                     flag=;
                     break;
                 }
                 node v=q.top();
                 q.pop();
                 if(timer<v.x||timer>v.y)
                 {
                     flag=;
                     break;
                 }
                 l[v.id]=timer;
                 timer++;
                 if(timer>n)break;
             }
         }
         for(int i=;i<n;i++)
             if(l[i]==||h[i]==)
             {
                 flag=;
                 break;
             }
         if(flag)
         {
             for(int i=; i<n; i++)
                 printf("%d %d\n",h[i],l[i]);
         }
         else puts("IMPOSSIBLE");
     }
     return ;
 }