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

int main(){
  int n;
  cin >> n;
  n *= 2;
  ll ans = -(1ll << 60);
  vector<ll> a(n), s0(n + 1), s1(n + 1);
  for(int i = 0; i < n; i++){
    cin >> a[i];
    s0[i + 1] = s0[i] + (i & 1 ? -a[i] : a[i]);
    s1[i + 1] = s1[i] + (i & 1 ? a[i] : -a[i]);
  }
  for(int i = 0; i <= n; i += 2){
    ans = max(ans, s0[i] + s1[n] - s1[i]);
  }
  cout << ans << '\n';
}