#include<bits/stdc++.h>
#define int long long
using namespace std;
int a,b;
int leftmax=0,rightmax=0;
int n;
signed main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a>>b;
		leftmax=max(leftmax,b);
		rightmax=max(rightmax,a-b);
	}
	cout<<leftmax+rightmax<<"\n";
	return 0;
}