#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n); i++)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
using P = pair<int, int>;
const int INF = 1e9;
const long long LINF = 1e18;
const long long MOD = 1e9 + 7;

signed main(){
    int n;
    cin >> n;
    int m = 2 * n;
    ll a[m];
    rep(i,m){
        cin >> a[i];
    }
    ll sumeven[m + 1] = {}, sumodd[m + 1] = {};
    for(int i = 0; i < m; i++){
        sumeven[i + 1] = sumeven[i] + (i % 2 == 0 ? a[i] : 0);
        sumodd[i + 1] = sumodd[i] + (i % 2 == 1 ? a[i] : 0);
    }
    ll ans = -LINF;
    for(int i = 0; i <= m; i += 2){
        ans = max(ans, sumeven[i] + sumodd[m] - sumodd[i] - (sumodd[i] + sumeven[m] - sumeven[i]));
    }
    cout << ans << endl;
    return 0;
}