#include <bits/stdc++.h>
#define whlie while
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define rep(i,N) for(int i = 0; i < (N); i++)
#define repr(i,N) for(int i = (N) - 1; i >= 0; i--)
#define rep1(i,N) for(int i = 1; i <= (N) ; i++)
#define repr1(i,N) for(int i = (N) ; i > 0 ; i--)
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
#define vrep(v,it) for(auto it = v.begin(); it != v.end(); it++)
#define vrepr(v,it) for(auto it = v.rbegin(); it != v.rend(); it++)
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) ll __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)
using namespace std; void solve();
using ll = long long; using vl = vector<ll>;
using vi = vector<int>; using vvi = vector< vector<int> >;
constexpr int inf = 1001001001;
constexpr ll infLL = (1LL << 61) - 1;
struct IoSetupNya {IoSetupNya() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(7);} } iosetupnya;
template<typename T, typename U> inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template<typename T, typename U> inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; }
template<typename T, typename U> ostream& operator <<(ostream& os, const pair<T, U> &p) { os << p.first << " " << p.second; return os; }
template<typename T, typename U> istream& operator >>(istream& is, pair<T, U> &p) { is >> p.first >> p.second; return is; }
template<typename T> ostream& operator <<(ostream& os, const vector<T> &v) { int s = (int)v.size(); rep(i,s) os << (i ? " " : "") << v[i]; return os; }
template<typename T> istream& operator >>(istream& is, vector<T> &v) { for(auto &x : v) is >> x; return is; }
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << "\n";} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}
#ifdef NyaanDebug
  #include "NyaanDebug.h"
  #define trc(...) do { cerr << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);} while(0)
  #define trca(v,N) do { cerr << #v << " = "; array_out(v , N);cout << endl;} while(0)
#else
  #define trc(...)
  #define trca(...)
  int main(){solve();}
#endif
using P = pair<int,int>; using vp = vector<P>;
constexpr int MOD = /** 1000000007; //*/ 998244353;
////////////////


void solve(){
  inl(N);
  vp v(N); in(v);
  sort( all(v) , [&]( P a,P b ){
    return a.fi == b.fi ? a.se > b.se : a.fi < b.fi;
  });
  // 右端をsetで管理
  map<ll,int> a , b;
  vl ans(N - 1) , bns(N - 1);
  // 切れ目は[0 , i)と[i , N)の間
  rep(i , N - 1){
    // 左から入れてく
    a[v[i].se]++;
    ans[i] = max(0LL , (*a.begin()).fi - v[i].fi + 1);
  }
  repr(i , N - 1){
    // 右から入れてく
    b[v[i + 1].se]++;
    bns[i] = max(0LL , (*b.begin()).fi - v[N - 1].fi + 1);
  }
  ll aaa = 0;
  rep(i , N - 1) amax(aaa , ans[i] + bns[i]);

  // 全部まし
  a[v[N-1].se]++;
  rep(i , N){
    // iを抜く
    if(--a[v[i].se] == 0) a.erase(v[i].se);
    ll cur = max(0LL , (*a.begin()).fi - v[(i == N - 1 ? N - 2 : N - 1)].fi + 1);
    amax(aaa , v[i].se - v[i].fi + 1 + cur);
    // iを入れる
    a[v[i].se]++;
  }
  out(aaa);
}

Measured memory_bytes: 15104