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