#include < iostream >
using   namespace  std;

struct  arr{
     int  x,y;
}a[ 1000 ];
int  n,f[ 1000 ];
int  cmp( const   void *  no1, const   void *  no2){
    arr  * nox = (arr * )no1, * noy = (arr * )no2;
     if (nox -> x  >  noy -> x)  return   1 ;
     else   if (nox -> x  <  noy -> x)  return   - 1 ;
     else   return  nox -> y - noy -> y;
}
int  main()
{
    scanf( " %d " , & n);
     for ( int  i = 0 ;i < n; ++ i) scanf( " %d%d " , & a[i].x, & a[i].y);
    qsort(a,n, sizeof (arr),cmp);
     int  MAX = 0 ;
     for ( int  i = 0 ;i < n; ++ i){
        f[i] = a[i].y - a[i].x + 1 ;
         for ( int  j = i - 1 ;j >= 0 ; -- j)
             if (a[i].x > a[j].y)
                 if (f[i] < f[j] + a[i].y - a[i].x + 1 )
                    f[i] = f[j] + a[i].y - a[i].x + 1 ;
          if (f[i] > MAX) MAX = f[i];
    }
    printf( " %d\n " ,MAX);
     return   0 ;
}