#include<bits/stdc++.h>
using namespace std;
long long n,a[1000000],b[1000000],ii,ma=-1000000,ma1=-1000000;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i]>>b[i];
		if(a[i]-b[i]<=b[i])
			a[i]=b[i];
		else
			a[i]-=b[i];
	}
	for(int i=1;i<=n;i++)
	{
		if(a[i]>ma)
			ma=a[i],ii=i;
	}
	for(int i=1;i<=n;i++)
	{
		if(a[i]>ma1&&i!=ii)
			ma1=a[i];
	}
	cout<<ma+ma1;
	
	return 0;
}