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

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

int main() {
  int n;
  cin >> n;
  vector<ll> a(2*n);
  rep(i,2*n) {
    cin >> a[i];
  }
  vector<ll> v(n);
  ll sum = 0;
  rep(i,n) {
    v[i] = a[2*i+1]-a[2*i];
    sum += v[i];
  }
  vector<ll> suml(n+1), sumr(n+1);
  rep(i,n) suml[i+1] = suml[i] + v[i];
  rep(i,n+1) sumr[i] = sum - suml[i];

  const ll INF = 1e18;
  ll ans = -INF;
  rep(i,n+1) ans = max(ans, sumr[i]-suml[i]);


  cout << ans << endl;
}