#include <bits/stdc++.h> using namespace std; #define TLHAdepzais1tg \ ios_base::sync_with_stdio(0); \ cin.tie(0); \ cout.tie(0); #define ll long long #define N 1000007 #define se second #define str string #define fi first #define se second #define pii pair<long long, int> int n; ll be[N]; ll pre[N]; ll ans = -1e18; ll ch[N], le[N]; int main() { TLHAdepzais1tg; if (fopen("BEAUTY.inp", "r")) { freopen("BEAUTY.inp", "r", stdin); freopen("BEAUTY.out", "w", stdout); } cin >> n; pre[0] = 0; for (int i = 1; i <= n; i++) { cin >> be[i]; pre[i] = pre[i - 1] + be[i]; } le[n + 1] = -1e18; ch[n + 1] = -1e18; for (int i = n; i >= 1; i--) { if (i % 2 == 0) { ch[i] = max(ch[i + 1], pre[i]); le[i] = le[i + 1]; } else { le[i] = max(le[i + 1], pre[i]); ch[i] = ch[i + 1]; } } for (int i = 1; i <= n - 3; i++) { if (i % 2 == 0) ans = max(ch[i + 4] - pre[i], ans); else ans = max(le[i + 4] - pre[i], ans); } cout << ans; return 0; }