# include <cstdio>
# include <algorithm>
# define MAXN 100005
using namespace std;
int a[MAXN],s[MAXN][2];
int n,i;

int main()
{
    freopen("oo.in", "r", stdin);
    freopen("oo.out", "w", stdout);
    scanf("%d", &n);
    for(i=1; i<=n; ++i) scanf("%d", &a[i]);
    s[1][0]=s[2][0]=s[3][0]=s[4][0]=a[1]+a[2];
    s[2][1]=0;
    for(i=5; i<=n-1; ++i)
    {
        s[i][0]=a[i]+a[i-1]+s[i-3][0];
        s[i][1]=max(s[i-1][0],s[i-1][1]);
    }
    printf("%d", max(s[n-1][0],s[n-1][1]));
    return 0;
}