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

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