#include<bits/stdc++.h>
#include<tr1/unordered_map>
#define ri register int
using namespace std;
#define fi first
#define se second
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> poly;
#define pb push_back
const int rlen=1<<18|1,inf=0x3f3f3f3f;
const ll Inf=1e18;
char buf[rlen],*ib=buf,*ob=buf;
#define gc() (((ib==ob)&&(ob=(ib=buf)+fread(buf,1,rlen,stdin)),ib==ob)?-1:*ib++)
inline int read() {
  int ans=0;
  bool f=1;
  char ch=gc();
  while(!isdigit(ch)) f^=ch=='-',ch=gc();
  while(isdigit(ch)) ans=((ans<<2)+ans<<1)+(ch^48),ch=gc();
  return f?ans:-ans;
}
inline ll readl() {
  ll ans=0;
  bool f=1;
  char ch=gc();
  while(!isdigit(ch)) f^=ch=='-',ch=gc();
  while(isdigit(ch)) ans=((ans<<2)+ans<<1)+(ch^48),ch=gc();
  return f?ans:-ans;
}
inline int Read(char*s) {
  int tp=0;
  char ch=gc();
  while(!isdigit(ch)&&!isalpha(ch)) ch=gc();
  while(isdigit(ch)||isalpha(ch)) s[++tp]=ch,ch=gc();
  return tp;
}
namespace modular {
  const int mod=1e9+7;
  inline int add(int a,int b) { return a+b<mod?a+b:a+b-mod; }
  inline int dec(int a,int b) { return a<b?a-b+mod:a-b; }
  inline int mul(int a,int b) { return (ll)a*b%mod; }
  inline void Add(int&a,int b) { a=a+b<mod?a+b:a+b-mod; }
  inline void Dec(int&a,int b) { a=a<b?a-b+mod:a-b; }
  inline void Mul(int&a,int b) { a=(ll)a*b%mod; }
  inline int ksm(int a,int p) { int ret=1;for(;p;p>>=1,Mul(a,a)) (p&1)&&(Mul(ret,a),1);return ret; }
  inline int Inv(int a) { return ksm(a,mod-2); }
  inline int sqr(int a) { return mul(a,a); }
  inline int cub(int a) { return (ll)a*a%mod*a%mod; }
}
using namespace modular;
template<typename T> inline void ckmax(T&a,T b) { a<b?a=b:0; }
template<typename T> inline void ckmin(T&a,T b) { a>b?a=b:0; }
template<typename T> inline T gcd(T a,T b) { T t;while(b)t=a,a=b,b=t-t/a*a;return a; }
template<typename T> inline T Abs(T x) { return x<0?-x:x; }
inline int rd() { return rand()|(rand()<<15); }
const int N=5e5+5;
int n,pre[N],suf[N];
pii a[N];
int main() {
  #ifdef ldxcaicai
  freopen("lx.in","r",stdin);
  #endif
  n=read();
  for(ri i=1;i<=n;++i) a[i].fi=read(),a[i].se=read();
  sort(a+1,a+n+1);
  pre[0]=0x3f3f3f3f,suf[n]=0x3f3f3f3f;
  for(ri i=1;i<n;++i) pre[i]=min(pre[i-1],a[i].se);
  for(ri i=n-1;i;--i) suf[i]=min(suf[i+1],a[i].se);
  int res=0;
  for(ri mn,r1,r2,t,i=1;i<n;++i) {
    r1=a[i].se,r2=min(max(suf[i+1],a[n].fi-1),a[n].se);
    t=(r1-a[i].fi+1)+(r2-a[n].fi+1);
    mn=pre[i-1];
    ckmax(res,t-max(0,min(r1-max(a[i].fi-1,mn),r2-max(a[n].fi-1,mn))));
  }
  cout<<res;
  return 0;
}
/*
 * @Author: RBQRBQ
 * @Date: 2020-04-05 15:08:15
 * @LastEditors: RBQRBQ
 * @LastEditTime: 2020-04-05 19:16:50
 */
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef pair<ll,ll> pii;
namespace IO{
    template<typename T>inline void read(T &x){
        x=0;ll f=1;char ch=getchar();
        while(!isdigit(ch)){if(ch=='-')f=-f;ch=getchar();}
        while(isdigit(ch)){x=x*10+ch-48;ch=getchar();}
        x=x*f;
    }
}
using namespace IO;
vector<pii> pp;
vector<pii> T;
ll mxL,minR,mxR,minL;


int main()
{
    int N;
    cin>>N;
    mxL=mxR=-1;
    minL=minR=10000000000ll;
    int P,Q;
    for(int i=1;i<=N;i++)
    {
        ll x,y;
        read(x),read(y);
        y++;
        pp.push_back(make_pair(x,y));
        if(x>mxL)
        {
            mxL=x;
            P=i;
        }
        if(minR>y)
        {
            minR=y;
            Q=i;
        }
    }
    ll ans1=0,ans2=0;
    minL=0;
    for(int i=1;i<=N;i++)
    {
            minL=max(minL,pp[i-1].second-pp[i-1].first);
    }

    ans1=max((minL),0ll)+max((minR-mxL),0ll);

    int ca=1;
    for(auto p:pp)
    {
        if(ca!=P&&ca!=Q)
        T.push_back(make_pair(max(p.second-mxL,0ll),max(minR-p.first,0ll)));
        ca++;
    }
    sort(T.begin(),T.end());
    ll P1=pp[P-1].second-pp[P-1].first;
    ll Q1=pp[Q-1].second-pp[Q-1].first;
    ll x1=0,x2=Q1;
    // for(auto p:T)
    // {
    //     cout<<p.first<<" "<<p.second<<endl;
    // }
    for(int i=0;i<T.size();i++)
    {
        
        x1=min(T[i].first,P1);
        ans2=max(ans2,x1+x2);
        x2=min(T[i].second,x2);
    }
    ans2=max(ans2,P1+x2);
    cout<<max(ans1,ans2);

}