#include<bits/stdc++.h> using namespace std; priority_queue<int>pq; int main(){ int n; cin>>n; for(int i = 1;i<=n;i++){ int a,b; cin>>a>>b; pq.push(b);pq.push(a-b); } int ans = pq.top(); pq.pop(); cout<<ans+pq.top()<<endl; }