#include <bits/stdc++.h>
using namespace std;

#define int long long
template<typename T>
void chmax(T &a,T b){
  if(a<b)a=b;
}

signed main(){
  int n;cin>>n;n*=2;
  vector<int> v(n);
  for(int i=0;i<n;i++)cin>>v[i];
  vector<int> w,ww;
  w.push_back(0);
  ww.push_back(0);
  for(int i=0;i<n;i+=2)w.push_back(w.back()+v[i]-v[i+1]);
  reverse(v.begin(),v.end());
  for(int i=0;i<n;i+=2)ww.push_back(ww.back()+v[i]-v[i+1]);
  int ans=-1e9;
  for(int i=0;i<w.size();i++)chmax(ans,w[i]+ww[ww.size()-1-i]);
  cout<<ans<<endl;
}