#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll n,a[114514],b[114514],b_a[114514],max1=0,maxb1=0,maxb_a1=0,maxb2=0,maxb_a2=0;
int main(){
	cin>>n;
	for(int i= 1;i<=n;i++){
		cin>>a[i]>>b[i];
		b_a[i]=a[i]-b[i];
		if(max1<a[i]){
			max1=a[i];
		}
		if(maxb1<b[i]){
			maxb1=b[i];
		}
		else if(maxb2<b[i]){
			maxb2=b[i];
		}
		if(maxb_a1<b_a[i]){
			maxb_a1=b_a[i];
		}
		else if(maxb_a2<b_a[i]){
			maxb_a2=b_a[i];
		}
	}
	if(maxb1+maxb_a1>max1){
		max1=maxb1+maxb_a1;
	}
	if(maxb1+maxb2>max1){
		max1=maxb1+maxb2;
	}
	if(maxb_a1+maxb_a2>max1){
		max1=maxb_a1+maxb_a2;
	}
	cout<<max1;
}