#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> l_l;
typedef pair<int, int> i_i;
template<class T>
inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}

const long double EPS = 1e-10;
const long long INF = 1e18;
const long double PI = acos(-1.0L);
//const ll mod = 1000000007;
ll N;
vector<ll> Asum, AOddSum;
ll sum = 0;

int main() {
    cin >> N;
    vector<ll> A(2 * N);
    Asum.resize(2 * N + 1);
    AOddSum.resize(2 * N + 1);
    for(int i = 0; i < 2 * N; i++) {
        cin >> A[i];
        Asum[i+1] = Asum[i] + A[i];
        AOddSum[i+1] = AOddSum[i];
        if(i & 1) AOddSum[i+1] += A[i];
    }
    for(int i = 0; i <= N; i++) {
        ll now = AOddSum[2 * N] - AOddSum[2*i];
        now += Asum[2*i] - AOddSum[2*i];
        chmax(sum, now);
    }
    cout << sum * 2 - Asum[2 * N] << endl;
    return 0;
}