#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;

#define scan(x) do{while((x=getchar())<'0'); for(x-='0'; '0'<=(_=getchar()); x=(x<<3)+(x<<1)+_-'0');}while(0)
char _;
#define complete_unique(a) a.erase(unique(a.begin(),a.end()),a.end())
#define all(a) a.begin(),a.end()
#define println printf("\n");
#define readln(x) getline(cin,x);
#define pb push_back
#define endl "\n"
#define INT_INF 0x3f3f3f3f
#define LL_INF 0x3f3f3f3f3f3f3f3f
#define MOD 1000000007
#define MOD2 1494318097
#define SEED 131
#define mp make_pair
#define fastio cin.tie(0); cin.sync_with_stdio(0);

#define MAXN 100005
#define LOGN 20

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef unordered_map<int,int> umii;
typedef pair<int,int> pii;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef pair<int,pii> triple;
typedef int8_t byte;

mt19937 g1(time(0));

int randint(int a, int b){return uniform_int_distribution<int>(a, b)(g1);}
ll randlong(ll a,ll b){return uniform_int_distribution<long long>(a, b)(g1);}

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);}
ll fpow(ll  b, ll exp, ll mod){if(exp == 0) return 1;ll t = fpow(b,exp/2,mod);if(exp&1) return t*t%mod*b%mod;return t*t%mod;}
ll divmod(ll i, ll j, ll mod){i%=mod,j%=mod;return i*fpow(j,mod-2,mod)%mod;}

int len,res,st[MAXN][LOGN];
vector<pii> segs;

inline bool cmp(pii a, pii b){
	if(a.second == b.second) return a.first<b.first;
	return a.second<b.second;
}

inline int query(int l, int r){
	int lg = (int)log2(r-l+1);
	return max(st[l][lg],st[r-(1<<lg)+1][lg]);
}

int main(){
	scanf("%d",&len);
	for(int i=1; i<=len; i++){
		int l,r; scanf(" %d %d",&l,&r);
		segs.pb(mp(l,r));
	}
	sort(all(segs)); complete_unique(segs);
	sort(all(segs),cmp);
	for(int i=0; i<segs.size(); i++)
		st[i][0] = segs[i].first;
	for(int sz=1; (1<<sz)<=segs.size(); sz++){
		for(int l=0; l+(1<<(sz-1))<segs.size(); l++){
			int f = st[l][sz-1], s = st[l+(1<<(sz-1))][sz-1];
			st[l][sz] = max(f,s);
		}
	}
	pii inter = segs[0];
	for(int i=1; i<segs.size()-1; i++){
		pii tmp = inter, tmp2 = segs[i];
		int smallest = query(i+1,(int)segs.size()-1);
		if(smallest > max(tmp.first,tmp2.first)){
			if(tmp.first > tmp2.first){
				res = max(res,tmp.second-tmp.first+1);
				tmp.first = smallest;
			}else{
				res = max(res,tmp2.second-tmp2.first+1);
				tmp2.first = smallest;
			}
		}
//		for(int k=i+1; k<segs.size(); k++){
//			if((segs[k].first <= tmp.first && tmp.first <= tmp.second) || segs[k].first <= tmp2.first) continue;
//			if(tmp.first > tmp.second) continue;
//			if(tmp.first >= tmp2.first) tmp.first = max(tmp.first,segs[k].first);
//			else tmp2.first = max(tmp2.first,segs[k].first);
//		}
		int f = max(0,tmp.second-tmp.first+1);
		int s = max(0,tmp2.second-tmp2.first+1);
		res = max(res,f+s);
		inter.first = max(inter.first,segs[i].first);
		if(inter.first > inter.second){
			int mx = 0;
			for(int k=i+1; k<segs.size(); k++)
				mx = max(mx,segs[k].second-segs[k].first+1);
			res = max(res,mx);
			break;
		}
	}
	int f = max(inter.second-inter.first+1,0);
	int s = segs.back().second-segs.back().first+1;
	res = max(res,f+s);
	printf("%d\n",res);
}
/*
3
1 4
2 20
18 21
ans=19
 */

Measured memory_bytes: 9076