#include<bits/stdc++.h>

using namespace std;
using ll=long long;
#define rep2(i, a, n) for(int i = (a); i < (n); i++)
#define rep(i, n) rep2(i,0,n)
#define infl 1LL<<60;

template<class T>
inline bool chmax(T& a, T b){if(a<b){a=b;return true;} return false;}

int main(){
  cin.tie(nullptr);ios_base::sync_with_stdio(false);
  int n;cin>>n;
  int a[n*2];
  rep(i,n*2)cin>>a[i];
  ll ans=-infl;
  ll tot=0;
  rep(i,n*2){
    if(i%2==0)tot-=a[i];
    else tot+=a[i];
  }
  chmax(ans,tot);
  rep(i,n){
		int first=a[i*2],second=a[i*2+1];
    tot+=first-second;
    tot+=first-second;
    chmax(ans,tot);
  }
  cout<<ans<<endl;
}