#include<bits/stdc++.h> __ 
using namespace std;
int n;
int main(){
	int x,y;
	cin>>n;
	int l=0,r=0,a,k1,k2,t1,t2,t3,t4;
	for(int i=0;i<n;i++){
		cin>>x>>y;
		a=x-y;
		t1=max(l,a);
		t2=max(r,y);
		k1=t1+t2;
		t3=max(l,y);
		t4=max(r,a);
		k2=t1+t2;
		if(k1>k2){
			l=t1;
			r=t2;	
		}else{
			l=t3;
			r=t4;
		}
	}
	cout<<l+r<<endl;
	return 0;
}