#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;
}
#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> ii;
typedef tuple<ll, ll, ll> iii;
typedef vector<ll> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<vi> vvi;
typedef vector<vii> vvii;
#define REP(i,n) for (ll i = 0; i < n; ++i)
#define REPR(i,n) for (ll i = n-1; i >= 0; --i)
#define FOR(i,m,n) for (ll i = m; i < n; ++i)
#define FORR(i,m,n) for (ll i = n-1; i >= m; --i)
#define FORE(x,xs) for (const auto& x : xs)
#define ALL(v) v.begin(), v.end()
#define CHMIN(x,y) x = min(x, y)
#define CHMAX(x,y) x = max(x, y)

const int MAX = 2e5+10;

int N;
vii lr;

ll solve() {
    ll mx = 0, mn = 1e10;
    ll ans = 0;
    FORE (x, lr) {
        CHMAX(mx, x.first);  // 最も右にある左端, X
        CHMIN(mn, x.second); // 最も左にある右端, Y
        CHMAX(ans, x.second - x.first); // 最長の区間
    }
    ans += max(0ll, mn - mx); // 最長以外を反対にした場合

    vii t;
    FORE (x, lr) {
        ll a = max(0ll, x.second - mx); // Xと同じグループにした時の範囲
        ll b = max(0ll, mn - x.first);  // Yと同じグループにした時の範囲
        t.push_back(make_pair(a, -b));
    }
    sort(ALL(t));
    REP (i, N) t[i].second *= -1;
    ll w = t[0].second;
    FOR (i, 1, N) {
        CHMAX(ans, w + t[i].first);
        CHMIN(w, t[i].second);
    }

    return ans;
}

int main() {
    cin >> N;
    REP (i, N) {
        int l, r;
        cin >> l >> r;
        lr.push_back(make_pair(l, r+1));
    }
    cout << solve() << endl;
}