#include <bits/stdc++.h>

#define INF 0x3f3f3f3f

using namespace std;

ifstream in("oo.in");
ofstream out("oo.out");

int n, rez;
int v[100001], dp1[100001], dp2[100001], dp3[100001];

inline void dinamica() {
    for (int i = 2; i <= n; ++i) {
        dp1[i] = max(dp1[i - 1], dp3[i - 1]);
        dp2[i] = dp1[i - 1] + v[i];
        dp3[i] = dp2[i - 1] + v[i];
    }
}

int main() {
    in >> n;
    for (int i = 1; i <= n; ++i)
        in >> v[i];
    dp1[1] = 0, dp2[1] = -INF, dp3[1] = -INF;
    dinamica();
    rez = max(rez, max(dp1[n], dp3[n]));
    dp1[1] = -INF, dp2[1] = v[1], dp3[1] = -INF;
    dinamica();
    rez = max(rez, dp1[n]);
    dp1[1] = -INF, dp2[1] = -INF, dp3[1] = v[1];
    dinamica();
    rez = max(rez, dp2[n]);
    return out << rez, 0;
}