#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
int a[100100],b[100100];
int main(){
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i]>>b[i];
		a[i]-=b[i];
	}
	sort(a+1,a+n+1);
	sort(b+1,b+n+1);
	if(b[n]==0)
	{
		cout<<a[n]+a[n-1];
	}
	else cout<<a[n]+b[n];
}