#include <bits/stdc++.h>
#include <unistd.h>
 
using namespace std;
 
typedef long long ll;
typedef pair<ll,ll> P;
 
long long int INF = 3e18;
const ll fact_table = 5000000;
double Pi = 3.1415926535897932384626;
 
vector<ll> G[550010];
//vector<P> tree[500010];
priority_queue <ll> pql;
priority_queue <P> pqp;
//big priority queue
priority_queue <ll,vector<ll>,greater<ll> > pqls;
priority_queue <P,vector<P>,greater<P> > pqps;
//small priority queue
//top pop
 
int dx[8]={1,0,-1,0,1,1,-1,-1};
int dy[8]={0,1,0,-1,1,-1,-1,1};
char dir[] = "DRUL";
//ll bit[500005];
//↓,→,↑,←
 
 
#define p(x) cout<<x<<"\n";
#define el cout<<endl;
#define pe(x) cout<<(x)<<" ";
#define ps(x) cout<<fixed<<setprecision(25)<<x<<endl;
#define pu(x) cout<<(x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)(); 
 

ll mod = 998244353;
//ll mod = 1000000007;
 
ll rui(ll number1,ll number2){
 
    if(number2 == 0){
        return 1;
    }else{
        ll number3 = rui(number1,number2 / 2);
        number3 *= number3;
        number3 %= mod;
        if(number2%2==1){
            number3 *= number1;
            number3 %= mod;
        }
        return number3;
    }
}
ll gcd(ll number1,ll number2){
 
    if(number1 > number2){
        swap(number1,number2);
    }
    if(number1 == 0 || number1 == number2){
        return number2;
    }else{
        return gcd(number2 % number1,number1);
    }
}
void YES(bool condition){
 
    if(condition){
        p("YES");
    }else{
        p("NO");
    }
    return;
}
void Yes(bool condition){

    if(condition){
        p("Yes");
    }else{
        p("No");
    }
    return;
}
 

ll fact[fact_table + 5],rfact[fact_table + 5];
 
void c3_init(){
    fact[0] = rfact[0] = 1;
    for(ll i=1; i<=fact_table; i++){
        fact[i] = (fact[i-1]*i) % mod;
    }
    rfact[fact_table] = rui(fact[fact_table],mod - 2);
    for(ll i=fact_table; i>=1; i--){
       rfact[i-1] = rfact[i] * i;
       rfact[i-1] %= mod;
    }
    return;}
ll c3(ll n,ll r){
    return (((fact[n] * rfact[r]) % mod ) * rfact[n-r]) % mod;}

 
ll n,m,num,sum,a,b,c,d,e,g,h,w,i,j,q,r,l;
ll k,idx,ans;
ll x[500005],y[500005],z[500005];
ll upl[500005],upr[500005];
ll downl[500005], downr[500005];
char s[500005];
P table[500005];

int main(){
    cin >> n;
    for(int i=0;i<n;i++){
        cin >> x[i] >> y[i];
        ans = max(ans, y[i] - x[i] + 1);
        table[i].first = x[i];
        table[i].second = y[i];
    }
    sort(table,table+n);
    upl[0] = table[0].first;
    upr[0] = table[0].second;
    for(int i=1;i<n;i++){
        upl[i] = max(upl[i-1], table[i].first);
        upr[i] = min(upr[i-1], table[i].second);
    }
    downl[n-1] = table[n-1].first;
    downr[n-1] = table[n-1].second;
    for(int i=n-2;i>=0;i--){
        downl[i] = max(downl[i+1], table[i].first);
        downr[i] = min(downr[i+1], table[i].second);
    }
    for(int i=0;i<n-1;i++){
        ll res = upr[i] - upl[i] + downr[i+1] - downl[i+1] + 2;
        ans = max(ans, res);
        if(i > 0){
            res = table[i].second - table[i].first + min(upr[i-1], downr[i+1]) - max(upl[i-1], downl[i+1]) + 2;
            ans = max(ans, res);
        }
    }



    p(ans);
    return 0;
}











Measured memory_bytes: 36352