#include <bits/stdc++.h>
#define pii pair<int,int>
#define fi first
#define se second
#define maxn 100000
//#define aaa system("pause");

using namespace std;

pii v[maxn+5];
pii dp[maxn+5]; ///dp[i]-timp maxim cu bandele 0..i (fi) capat dreapta (se)

bool cmp ( pii a, pii b )
{
  if ( a.se != b.se ) return a.se < b.se;
  return a.fi < b.fi;
}

int main ()
{
  ifstream fin ( "heavymetal.in" );
  ofstream fout ( "heavymetal.out" );

  int n; fin >> n;

  int i, j, z, itv, _M = 0, pas;
  for ( i = 0; i < n; i++ ) fin >> v[i].fi >> v[i].se;
  sort ( v, v + n, cmp );

  for ( i = 0; i < n; i++ )
  {
    itv = v[i].se-v[i].fi;
    dp[i] = {itv,v[i].se};
    for ( j = 0, pas = (1<<20); pas > 0; pas /= 2 )
      if ( j + pas < i && dp[j+pas].se <= v[i].fi && dp[i].fi < dp[j+pas].fi + itv ) j += pas;

    if ( dp[j].fi > 0 ) dp[i] = {dp[j].fi + itv - (dp[j].se==v[i].fi),v[i].se};
    _M = max(_M, dp[i].fi);
  }

  fout << _M;

  fin.close ();
  fout.close ();

  return 0;
}