#include <bits/stdc++.h>
#define int ll
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define rng(i,c,n) for(int i=c;i<n;i++)
#define fi first
#define se second
#define pb push_back
#define all(a) a.begin(), a.end()
#define sz(a) ((int) a.size())
#define vec(...) vector<__VA_ARGS__>
#define _3TpP2FO ios::sync_with_stdio(0),cin.tie(0);
typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pii;
void print(){cout<<'\n';}
template<class h,class...t>
void print(const h&v,const t&...u){cout<<v<<' ',print(u...);}

const int inf=1e9;

void slv(){
	int n;
	cin>>n;

	vec(pii) a(n);
	rep(i,n){
		cin>>a[i].fi>>a[i].se;
	}
	sort(all(a));

	int lk=-inf;
	rep(i,n){
		auto [l,r]=a[i];
		// l - i - 1 <= k
		lk=max(lk,l-i-1);
	}
	//print(lk);

	auto f=[&](int k)->int{
		vec(vi) adqry(n+1);
		rep(i,n){
			auto [l,r]=a[i];
			l-=k,r-=k;
			l=max(l,1ll);
			r=min(r,n);
			if(l>r) return 0;
			adqry[l].pb(r);
		}
		priority_queue<int,vec(int),greater<int>> pq;
		rng(l,1,n+1){
			for(auto r:adqry[l]) pq.push(r);
			while(sz(pq) and pq.top()<l) pq.pop();
			if(!sz(pq)) return 0;
			pq.pop();
		}
		return 1;
	};
	if(!f(lk)){
		print(0);
		return;
	}

	int l=lk,r=inf;
	int rk=lk;
	while(l<=r){
		int m=(l+r)/2;
		if(f(m)) rk=m,l=m+1;
		else r=m-1;
	}
	print(rk-lk+1);
}

signed main(){
_3TpP2FO;
	slv();
}