#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin >> N;
  vector<int64_t> A(2 * N);
  for (auto&& e : A) {
    cin >> e;
  }
  vector<int64_t> B(2 * N + 1, 0), C(2 * N + 1, 0);
  for (int i = 0; i < 2 * N; i += 2) {
    B[i] += A[i] - A[i + 1];
    C[i] += A[i + 1] - A[i];
    B[i + 2] += B[i];
    C[i + 2] += C[i];
  }
  int64_t res = max(B.back(), C.back());
  for (int i = 0; i < 2 * N; i += 2) {
    res = max(res, B[i] + C.back() - C[i]);
  }
  cout << res << '\n';
  return 0;
}