#include<bits/stdc++.h> using namespace std; int n; int a[100005],b[100005],c[100005]; int main(){ cin>>n; int ans=0; for(int i=1;i<=n;i++){ cin>>a[i]>>b[i]; ans=max(ans,a[i]); c[i]=max(a[i]-b[i],b[i]); } sort(c+1,c+n+1); cout<<max(c[n]+c[n-1],ans); return 0; }