#include<bits/stdc++.h>
using namespace std;
struct md
{
	int k,dk;
}kk[100005];
int n,k[100005],a,b,dk[100005];
bool cmp(md x,md y)
{
	return x.k>y.k;
}
int main()
{
	cin>>n;
	if(n==1)
	{
		cin>>a>>b;
		cout<<max(a-b,b);
		return 0;
	}
	for(int i=1;i<=n;i++)
	{
		cin>>a>>b;
		kk[i].k=max(b,a-b);
		kk[i].dk=min(b,a-b);
	}
	sort(kk+1,kk+n+1,cmp);
	if(kk[1].dk>kk[2].k) cout<<kk[1].k;
	else cout<<kk[1].k+kk[2].k;
 	return 0;
}