#include <iostream>
#include <iomanip>
#include <string>
#include <stack>
#include <vector>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <regex>
using namespace std;
using pii  = pair<int,int>;
using ll=long long;
using ld=long double;
#define pb push_back
#define mp make_pair
#define stpr setprecision
#define cYES cout<<"YES"<<endl
#define cNO cout<<"NO"<<endl
#define cYes cout<<"Yes"<<endl
#define cNo cout<<"No"<<endl
#define rep(i,n) for(ll i=0;i<(n);++i)
#define Rep(i,a,b) for(ll i=(a);i<(b);++i)
#define rrep(i,n) for(int i=n-1;i>=0;i--)
#define rRep(i,a,b) for(int i=a;i>=b;i--)
#define crep(i) for(char i='a';i<='z';++i)
#define psortsecond(A,N) sort(A,A+N,[](const pii &a, const pii &b){return a.second<b.second;});
#define ALL(x) (x).begin(),(x).end()
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define endl '\n'
int ctoi(const char c){
  if('0' <= c && c <= '9') return (c-'0');
  return -1;
}
ll gcd(ll a,ll b){return (b == 0 ? a : gcd(b, a%b));}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}
constexpr ll MOD=1000000007;
constexpr ll INF=1000000011;
constexpr ll MOD2=998244353;
constexpr ll LINF = 1001002003004005006ll;
constexpr ld EPS=10e-8;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
template<typename T> istream& operator>>(istream& is,vector<T>& v){for(auto&& x:v)is >> x;return is;}
template<typename T,typename U> istream& operator>>(istream& is, pair<T,U>& p){ is >> p.first; is >> p.second; return is;}
template<typename T,typename U> ostream& operator>>(ostream& os, const pair<T,U>& p){ os << p.first << ' ' << p.second; return os;}
template<class T> ostream& operator<<(ostream& os, vector<T>& v){
    for(auto i=begin(v); i != end(v); ++i){
        if(i !=begin(v)) os << ' ';
        os << *i;
    }
    return os;
}

int main(){
    ll N,L,R,l[100007],r[100007],li,ri,ran=-1;
    pair<ld,pair<ld,ld>> P[100007];
    cin >> N;
    rep(i,N){
        cin  >> P[i].second.first >> P[i].second.second;
        ran=max(ran,(ll)P[i].second.second-(ll)P[i].second.first+1);
        P[i].first=P[i].second.second-P[i].second.first+1;
    }

    sort(P,P+N);

    l[0]=P[0].second.second-P[0].second.first+1;
    li=P[0].second.first;ri=P[0].second.second;
    rep(i,N-1){
        li=max(li,(ll)P[i+1].second.first);
        ri=min(ri,(ll)P[i+1].second.second);
        l[i+1]=max(ri-li+1,0LL);
    }
    r[N-1]=P[N-1].second.second-P[N-1].second.first+1;
    li=P[N-1].second.first;ri=P[N-1].second.second;
    rRep(i,N-2,0){
        li=max(li,(ll)P[i].second.first);
        ri=min(ri,(ll)P[i].second.second);
        r[i]=max(ri-li+1,0LL);
    }
    ll  ma=-1;
    rep(i,N-1){
        ma=max(l[i]+r[i+1],ma);
    }

    rep(i,N){
        P[i].first=(P[i].second.first+P[i].second.second)/2;
    }

    sort(P,P+N);

    l[0]=P[0].second.second-P[0].second.first+1;
    li=P[0].second.first;ri=P[0].second.second;
    rep(i,N-1){
        li=max(li,(ll)P[i+1].second.first);
        ri=min(ri,(ll)P[i+1].second.second);
        l[i+1]=max(ri-li+1,0LL);
    }
    r[N-1]=P[N-1].second.second-P[N-1].second.first+1;
    li=P[N-1].second.first;ri=P[N-1].second.second;
    rRep(i,N-2,0){
        li=max(li,(ll)P[i].second.first);
        ri=min(ri,(ll)P[i].second.second);
        r[i]=max(ri-li+1,0LL);
    }
    rep(i,N-1){
        ma=max(l[i]+r[i+1],ma);
    }

    cout << max(ma,ran) << endl;
}

Measured memory_bytes: 6528