// template version 1.13
using namespace std;
#include <bits/stdc++.h>

// varibable settings
#define infile "../test/sample-1.in"
#define int long long //{{{
const int INF=1e18;
const int MOD=1e9+7; //}}}

// define basic macro {{{
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,n) rrepi(i,0,n)
#define rrepi(i,a,b) for(int i=(int)((b)-1);i>=(int)(a);--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define each(i,a) for (auto&& i : a)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define mt(a, b, c) make_pair(a, b, c)
#define ceil(a,b) ((a)+(b)-1)/(b)
#define is_in(x, a, b) ((a)<=(x) && (x)<(b))
#define uni(x) sort(all(x));x.erase(unique(all(x)),x.end())
#define ub upper_bound
#define lb lower_bound
#define posl(A, x) (lower_bound(all(A), x)-A.begin())
#define posu(A, x) (upper_bound(all(A),x)-A.begin())
template<class T> inline void chmax(T &a, const T &b) { if((a) < (b)) (a) = (b); }
template<class T> inline void chmin(T &a, const T &b) { if((a) > (b)) (a) = (b); }

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int,int> pii;
typedef tuple<int,int,int> iii;

template<typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;
struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast;

#if defined(PCM) || defined(LOCAL)
  #include "lib/dump.hpp"
#else
  #define dump(...) 42
  #define dump_1d(...) 42
  #define dump_2d(...) 42
#endif
//}}}

int solve(){
  int n;cin>>n;
  vi L(n); vi R(n);
  vector<pii> LR;
  int M = 0;
  rep(i,n){
    cin>>L[i]>>R[i];
    LR.pb(mp(L[i], R[i]));
    chmax(M, R[i]-L[i]+1);
  }
  sort(all(LR));
  dump(LR);
  dump(M);

  if (n<=20){
    int res = M;
    rep(mask, 1<<n){
      int p = 0;
      int q = 0;
      int l1=-INF, r1=INF;
      int l2=-INF, r2=INF;
      rep(i, n){
        if (mask&(1<<i)){
          chmax(l1, L[i]);
          chmin(r1, R[i]);
          p++;
        }
        else{
          chmax(l2, L[i]);
          chmin(r2, R[i]);
          q++;
        }
      }
      int ans = max(r1-l1+1,0LL) + max(r2-l2+1, 0LL);
      if (p && q) chmax(res, ans);
    }
    cout << res << endl;
    return 0;
  }

  vi L1(n, -INF), R1(n, INF);
  rep(i, 0, n){
    if (i>0){
      L1[i] = L1[i-1];
      R1[i] = R1[i-1];
    }
    chmax(L1[i], LR[i].first);
    chmin(R1[i], LR[i].second);
  }
  dump(L1);
  dump(R1);

  vi L2(n, -INF), R2(n, INF);
  rrep(i, 0, n){
    if (i<n-1){
      L2[i] = L2[i+1];
      R2[i] = R2[i+1];
    }
    chmax(L2[i], LR[i].first);
    chmin(R2[i], LR[i].second);
  }
  dump(L2);
  dump(R2);

  int res = M;
  rep(i, 0, n-1){
    int ans = max(R1[i]-L1[i]+1,0LL) + max(R2[i+1]-L2[i+1]+1, 0LL);
    dump(i, max(R1[i]-L1[i]+1,0LL), max(R2[i+1]-L2[i+1]+1, 0LL), ans);
    chmax(res, ans);
  }

  rep(i, 1, n-1){
    int ans = 0;
    ans += R[i]-L[i]+1;
    ans += max(min(R1[i-1], R2[i+1])-max(L1[i-1],L2[i+1])+1,0LL);
    chmax(res, ans);
  }

  cout << res << endl;

  return 0;
}

signed main() { //{{{
#ifdef INPUT_FROM_FILE
  std::ifstream in(infile);
  std::cin.rdbuf(in.rdbuf());
#endif
  solve();
  return 0;
} //}}}


Measured memory_bytes: 6512