#include <bits/stdc++.h>
#define int long long
const int NMAX = 1e5;
using namespace std;
ifstream fin ("oo.in");
ofstream fout ("oo.out");
int v[NMAX + 5], n;
int caz1(){
    int dp[NMAX + 5] = {0};
    dp[2] = v[1] + v[2];
    for (int i = 3; i <= n - 1; ++i)
         dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    return dp[n - 1];
}
int caz2(){
    int dp[NMAX + 5] = {0};
    dp[3] = v[2] + v[3];
    for (int i = 4; i <= n; ++i)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    return dp[n];
}
int caz3(){
    int dp[NMAX + 5] = {0};
    dp[4] = v[3] + v[4];
    for (int i = 5; i <= n + 1; ++i)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    return dp[n + 1];
}
signed main(){
    fin >> n;
    for (int i = 1; i <= n; ++i)
        fin >> v[i];
    fout << max({caz1(), caz2(), caz3()});
    return 0;
}