#include < iostream >
using   namespace  std;

struct  arr{
     int  x,y;
}a[ 101 ];
int  N;
int  f[ 101 ] = { 0 };
int  cmp( const   void *  no1, const   void *  no2){
    arr  * nox = (arr * )no1, * noy = (arr * )no2;
     return  nox -> y - noy -> y;
}
int  main()
{
    cin >> N;
     for ( int  i = 0 ;i < N; ++ i){
        cin >> a[i].x >> a[i].y;
         if (a[i].x > a[i].y){
             int  tmp = a[i].x;
            a[i].x = a[i].y;
            a[i].y = tmp;
        }
    }
    qsort(a,N, sizeof (arr),cmp);
     int  ans = 0 ;
     for ( int  i = 0 ;i < N; ++ i)
         if ( ! f[i]){
             for ( int  j = i + 1 ;j < N; ++ j)
                 if ( ! f[j] && a[i].y > a[j].x)
                    f[j] = 1 ;
            ans ++ ;
        }
    cout << ans << endl;
     for ( int  i = 0 ;i < N; ++ i)
         if ( ! f[i])
            cout << a[i].x << "   " << a[i].y << endl;
     return   0 ;
}