#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#include <tuple>
#define mkp make_pair
#define mkt make_tuple
#define rep(i,n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
const ll MOD=1e9+7;
template<class T> void chmin(T &a,const T &b){if(a>b) a=b;}
template<class T> void chmax(T &a,const T &b){if(a<b) a=b;}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int N;
  cin>>N;
  int M=2*N;
  vector<ll> A(M);
  rep(i,M) cin>>A[i];

  vector<ll> lef(M+1,0),rig(M+1,0);
  for(int i=0;i<M;i++){
    lef[i+1]=lef[i];
    if(i%2) continue;
    lef[i+1]+=A[i]-A[i+1];
  }
  for(int i=M-1;i>=0;i--){
    rig[i]=rig[i+1];
    if(i%2==0) continue;
    rig[i]+=A[i]-A[i-1];
  }

  ll ans=-MOD;
  for(int i=0;i<=M;i+=2){
    chmax(ans,lef[i]+rig[i]);
  }
  cout<<ans<<endl;

  return 0;
}