#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,sse3,sse4,popcnt,abm,mmx")

#include <bits/stdc++.h>   
#include <stdio.h>    
 
using namespace std;
     
#define F first
#define S second
#define lb lower_bound               
#define ub upper_bound
#define pb push_back
#define pf push_front    
#define ppb pop_back
#define mp make_pair
#define bpp __builtin_popcountll                                                                                        
#define sqr(x) ((x) * (x)) 
#define al 0x3F3F3F3F
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define in insert
#define ppf pop_front
#define endl '\n'
//#define int long long
 
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef pair <int, int> pii;
 
const int mod = (int)1e9 + 7;
const int N = (int)2e5 + 123;
const ll inf = (ll)3e18 + 1;

const double pi = acos (-1.0);
const double eps = 1e-7;                  
const int dx[] = {0, 0, 1, 0, -1};
const int dy[] = {0, 1, 0, -1, 0};

int n, ans;
pii r[N];
multiset <int> l1, r1;

inline void boost () {                    
   ios_base :: sync_with_stdio (NULL);
   cin.tie (NULL), cout.tie (NULL);          
}                                                     

inline void Solve () {
   cin >> n;
   for (int i = 1; i <= n; i ++) {
      cin >> r[i].F >> r[i].S;
      l1.in (r[i].F);
      r1.in (r[i].S);
      ans = max (ans, r[i].S - r[i].F + 1);
   }
   sort (r + 1, r + n + 1);
   int pos = 1;
   for (int i = 1; i <= n; i ++)
      if (r[pos].S < r[i].F) {
         if (pos > 1) {
            cout << ans, exit (0);
         }
         pos = i;
      }
   if (pos == 1) {
      int res = 0, L = 1, R = 1000000000, mn = mod;
      for (int i = 1; i <= n; i ++) {
         l1.erase (l1.find (r[i].F));
         r1.erase (r1.find (r[i].S));
         ans = max (ans, r[i].S - r[i].F + 1 + *r1.begin () - *l1.rbegin () + 1);
         l1.in (r[i].F);
         r1.in (r[i].S);
         if (i > 1 && min (r[1].S, r[i].S) - max (r[1].F, r[i].F) < mn) {
            mn = min (r[1].S, r[i].S) - max (r[1].F, r[i].F);
            pos = i;
         }
      }
   }
   multiset <int> l2, r2;
   l1.clear (), r1.clear ();
   for (int i = 1; i <= n; i ++) {
      if (pos == i) {
         for (int j = 1; j <= n; j ++)
            if (i != j)
               l1.in (r[j].F), r1.in (r[j].S);
         l2.in (r[i].F);
         r2.in (r[i].S);
         for (int j = n; j > 1; j --) {
            ans = max (ans, *r2.begin () - *l2.rbegin () + 1 + *r1.begin () - *l1.rbegin () + 1);
            if (j == i) continue;
            l1.erase (l1.find (r[j].F));
            r1.erase (r1.find (r[j].S));
            l2.in (r[j].F);
            r2.in (r[j].S);
         }
         ans = max (ans, *r2.begin () - *l2.rbegin () + 1 + *r1.begin () - *l1.rbegin () + 1);
      }
   }
   cout << ans;
}                                     


main () {                                       
// freopen (".in", "r", stdin);    
// freopen (".out", "w", stdout);              
   boost ();
   int tt = 1;
   //cin >> tt;   
   while (tt --) {
      Solve ();
   }                                               
   return 0;      
}


Measured memory_bytes: 10368