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

int main() {
  long N;
  cin >> N;
  N *= 2;
  vector<long> A(N);
  for (long i = 0; i < N; i++) cin >> A.at(i);

  long M = N / 2 + 1;
  vector<long> L(M), R(M);
  for (long i = 1, j = 0, sum = 0; i < M; i++) L.at(i) = sum += A.at(j) - A.at(j + 1), j += 2;
  reverse(A.begin(), A.end());
  for (long i = 1, j = 0, sum = 0; i < M; i++) R.at(i) = sum += A.at(j) - A.at(j + 1), j += 2;
  reverse(R.begin(), R.end());

  long ans = 0;
  for (long i = 1; i + 1 < M; i++) ans = max(ans, L.at(i) + R.at(i));
  cout << ans << "\n";
}